RESEARCHHIGHLIGHTS 2019
A publication of the WPI Advanced Institute for Materials ResearchTABLE OF CONTENTSMESSAGE FROM
THE DIRECTOR
1

11 Nanoporous graphene: High strength andflexibility achieved

Pursuing excellence in materials science on a global stage

graphene on edge

Director’s interview: Building on an impressive legacy

RESEARCH HIGHLIGHTS
5
6
7
8
9

Neuroscience: Neuronal networks in dishes
Crystal structure: Fourth crystallographic phase uncovered
Spintronics: Magnetic tunnel junctions go ferrimagnetic
Lithium batteries: Electrode boosts storage capacity
Lithium batteries: Complex hydride promising as
solid electrolyte

10 Topological phases: Two new fermions discovered

WPI Advanced Institutefor Materials Research
The Advanced Institute for Materials
Research (AIMR) at Tohoku University
in Sendai, Japan, was launched in 2007 as
one of the centers established by the World
Premier International Research Center
Initiative (WPI) with the support of theJapanese Ministry of Education, Culture,
Sports, Science and Technology (MEXT).
Since then, the AIMR has been bringing
together world-class researchers fromJapan and abroad to carry out cuttingedge research in materials science throughinterdisciplinary collaboration among its
four materials-related groups — Materials
Physics, Non-equilibrium Materials, Soft
Materials, Device/System — and theMathematical Science Group.

on a multilayer structure

13 Electrochemical water splitting: Mathematically designed

SPECIAL SECTION
2

12 Topological insulators: Imaging nanoscale domains

14 Magnetic materials: A magnet that can twist and turn
15 Metallic glasses: Discovering better combinations faster16 Fuel-cell catalysts: Surpassing platinum
17 Iron-based superconductors: Ruling out a cause
for high-temperature superconductivity

IN THE SPOTLIGHT

19 Seeking synergies between fields and countries
22	Promoting interaction between material scientists in
Europe and Japan

In 2017, the AIMR became a memberof the WPI Academy, which consists of
WPI centers that have achieved worldpremier status. The institute will continue
to maintain its world-class research
environment and further promote global
brain circulation.
Led by distinguished materialscientist and director Shin-ichi Orimo,
the institute promotes interdisciplinary
research across the different groups. It
also fosters young researchers throughthe Global Intellectual Incubation andIntegration Laboratory (GI3 Lab). This
unique program, which is currently
supported by the WPI Academy,
promotes international joint research
conducted in close cooperation withhigh-profile researchers invited fromcountries around the world.

The AIMR is host to about 100 leading
researchers, around 40 percent of whomcome from abroad, including 25 principal
and junior principal investigators. In
addition to the research hub at Tohoku
University, the AIMR collaborates withresearch centers in China, Germany,
Poland, the UK and the US. Close ties
with other leading overseas institutes aremaintained, going along with the efforts
of foreign principal and junior principal
investigators, as well as adjunct professors
and associate professors.

MESSAGE FROM THE DIRECTOR

Pursuing excellencein materials scienceon a global stage
The Advanced Institute for Materials Research (AIMR)

on Materials Science and Spintronics in February 2019.

was founded in 2007 with support from the World Premier

It was attended by more than 250 researchers from seven

International Research Center Initiative (WPI), a Japanesecountries. Particularly notable among the 18 guest speakers

government program for establishing world-class researchwere Professor Alan Lindsay Greer of the University ofcenters. Since then, AIMR has been advancing WPI’s four ob-

Cambridge in the UK, principal investigator at AIMR andjectives: advancing top-level research, creating interdisciplin-a world authority on microstructure formation of metallic

ary domains, establishing international research environments,

materials, and Professor Kang L. Wang of the University ofand reforming research organizations. It has become a center

California, Los Angeles, who is celebrated worldwide forfor materials science that attracts outstanding researchers fromhis discovery of chiral Majorana fermions and spintronics

all over the world. In 2017, AIMR became a member of theresearch. Stimulating discussions took place about the

newly established WPI Academy, and has maintained world-very latest research on materials science and spintronics —class standards as it drives efforts to accelerate and expand the

AIMR’s key focus since its founding.

international circulation of the world’s best brains.

In May 2019, AIMR partnered with three otherAs an international center for materials science, AIMR

materials-related WPI centers to run a joint booth at thestands out through its ambition to promote collaboration

European Materials Research Society (E-MRS) Spring

between mathematics and materials science. By employing

Meeting in Nice, France. This enabled AIMR to interact

the universal language of mathematics to describe the ex-with many researchers from all over Europe. In thetremely broad field of materials science, we aim to identify

following month of June, the French CNRS National

the commonalities among a variety of materials and pursue

Competency Cluster in Nanoscience (C’Nano) joined the

new topics to produce novel research outcomes. Institute-four WPI centers, which included AIMR, to hold the 13th

level initiatives that seek to establish collaborations between

Japan–France Workshop on Nanomaterials and the 4thmathematicians and materials scientists are rare; and our

WPI Workshop on Materials Science (NanoMat 2019)

efforts are emblematic of AIMR’s status as a progressive

in Paris, France. At this workshop, French and Japanese

center for materials science.

researchers gave presentations, furthering their research-

Having been officially recognized by the Japanese govern-

based exchange. Through multinational events such as

ment as a Designated National University in June 2017,

these, AIMR is strengthening its global network and foster-

Tohoku University is expected to pursue educational anding an international outlook, both of which are among its

research activities at the highest international level as one of

key objectives.

Japan’s leading universities. The university is making steady

I would like to thank all those who have lent us theirprogress in bolstering its research capabilities by establishingsupport. At AIMR, we are playing a central role in Tohoku

core research clusters in four fields: materials science, spin-

University’s efforts to establish an international research en-tronics, next-generation medicine and disaster science. AIMR

vironment as a Designated National University. We intend

is playing a leading role in establishing the materials science

to redouble our efforts to pursue high-quality research as a

research cluster, collaborating with other institutes andhub facilitating international circulation of the world’s best

departments to launch five new projects on energy materials,

brains, and contribute to cutting-edge materials science andelectronic materials, biomaterials, materials development

societal advancement.

based on texture control, and high-strength materials.
To advance these activities, AIMR partnered with the
spintronics research cluster to hold the 2nd Symposium

Shin-ichi Orimo, Director
Advanced Institute for Materials Research, Tohoku University

SPECIAL SECTION

DIRECTOR’S INTERVIEW

Published online on 23 December 2019

Building on an impressive legacy
Shin-ichi Orimo, who assumed the helm of the AIMR earlier this year, shares his vision for the institute’s futureI

n October 2019, Professor Shin-ichi
Orimo became the third director of
the Advanced Institute for Materials
Research (AIMR) at Tohoku University
in its 12-year history. He succeeded
Professor Motoko Kotani, who had been
director of the AIMR since 2012. They
are big shoes to fill. “Under her guidance,
researchers at the AIMR produced many
outstanding results,” Orimo notes. “Theexcellent quality of this research brought
us worldwide recognition.”
But Orimo is ideally positioned to assume the directorship of the AIMR. Fora start, he has enjoyed a long relationshipwith the AIMR. His laboratory at theInstitute of Materials Research, whichis also at Tohoku University and just a
short stroll from the AIMR, is seeking toresearch and develop hydrogen functional
materials for energy devices such as fuelcells and all-solid-state secondary batteries. Over the years, his team has collaborated extensively with AIMR researchers.
“As the leader of the Device/System Groupat the AIMR, I have participated in many
joint research projects and have strengthened collaboration with others on our
teams,” Orimo says.
Continuing an interdisciplinary legacy
Orimo is keen to continue the interdisciplinary emphasis that the AIMR has
been focusing on, namely the two-way
interaction between mathematics andmaterials science. “This approach has
more than proved its worth,” he says.
“My aim is to further advance the collaboration between mathematics andmaterials science and to link this to thecreation of new materials.”2

Orimo’s vision is to use materials science toprovide various solutions to the problems faced bysociety today.

Orimo is very conscious of the valuable insights that mathematics can bringto materials science through his own
research topic. “Molecular dynamics
calculations are extensively used toinvestigate ion mobility in materials,”
he explains. “At the AIMR, we are using
a mathematical perspective to identify
structural characteristics with a focus on
mobility randomness to obtain a more
fundamental understanding.” This is justone example of the symbiotic relationshipbetween the two fields: “We are really interested in two-way research, namely theapplication of mathematics to materials,
and materials to mathematics.”
One practical link being forged between mathematics and materials scienceis the recent appointment of a renowned
mathematician, Professor Hiroshi Suito,
as deputy director of the AIMR. He is aleader at the Mathematical Science Groupof the AIMR.

Another conduit is the establishment of three Advanced Target Projects(ATPs) that will address the control of
local structure in topological functional
materials; the integrated control of bondvariation and its time evolution; and improving self-organization technology andcontrolling biological responses. “These
projects not only build on the knowledge
and methods gained in AIMR’s conventional research, but they also go further
by employing mathematical techniquesthat are easier to apply to material
creation,” Orimo says. He notes that thethree ATPs respectively address phenomena on the micro, meso and macro scales.
“Our ultimate goal is to create materials
based on a complete understanding andcontrol of atoms and molecules — thesmallest units for materials,” Orimo says.
“To reach this goal, the ATPs aim to create materials that express new functions
by connecting our understanding andability to precisely control atoms andmolecules to phenomena on the meso
and macro scales.”Enhancing international collaboration
Another major emphasis of the AIMR
has been the adoption of a global outlook
through strengthening ties with overseas
researchers and institutes. The institutehas established three joint laboratories
with overseas institutions: one with the
University of Cambridge in the UK witha focus on non-equilibrium materials
and computational materials science,
another with the University of Chicago
in the US that specializes in spintronics,
and a third with Tsinghua University in
China focusing on topological materials.

AIMResearch 2019

Shin-ichi Orimo iseager to develop evenstronger ties between the
AIMR and industry.

Orimo intends to continue to pursue
international collaboration. “I hope todevelop exchange relationships withoverseas universities and research institutions, especially those in Switzerland andFrance,” he says.

he comments. “Collaborating with industry is critical for creating materials that
contribute to society.”“MY VISION IS TO
LEAD THE AIMR TO
Strengthening partnership between
THE NEXT STAGE
academia and industry
AS THE WORLD’SThe AIMR has an excellent track record of applying research outcomes to inLEADING INSTITUTE
dustrially relevant problems. Orimo is no
FOR MATERIALS
stranger to collaboration with industry.
SCIENCE.”His research team has collaborated with awide range of companies, including thosein the materials, electricity and vehicleindustries. And he is working on creatinga research platform between industry andacademia. “I want to deepen cooperation
with industry by further strengthening
ties with university–industry collaborative organizations at Tohoku University,”

AIMResearch 2019

Focusing on ‘three Rs’
Speaking of his vision for his directorship,
Orimo refers to ‘three Rs’: Relief, Researchand Recognition. The first ‘R’, Relief, refers
to the holistic welfare of everyone at theinstitute, including their physical safety
and mental well-being. The second ‘R’

is for research, which must stay as close
to the frontiers of current knowledge as
possible. “Being at the edge of the research
front means being at a cliff edge at thesame time,” Orimo explains. “It is crucial
that we always stay alert to that fact.”
Finally, the third ‘R’ is recognition, which
involves actively publicizing research
results, so that the AIMR gains an evenhigher profile both in Japan and abroad.
“My vision is to lead the AIMR to thenext stage as the world’s leading institutefor materials science by strengthening
collaboration between materials scienceand mathematics, while advancing thediscovery and development of new materials through the utilization of advanced
measurement technologies,” explains
Orimo. “In light of the problems we face
today, I hope to provide various solutions
in collaboration with our members,”
he adds.” n3

RESEARCH HIGHLIGHTS
The AIMR advances research in materials physics, non-equilibrium materials, soft materials and devices/
systems, and actively promotes collaboration among these divisions toward the development of groundbreaking technologies that cross the boundaries of conventional fields of study — bridging the disciplinesof materials science, physics, chemistry and precision, mechanical, electronics and information engineering.
The Mathematical Science Group further complements the AIMR’s research activities.

RESEARCH HIGHLIGHTS

Neuroscience:

Neuronal networks in dishes

By precisely engineering the interface
between living cells and a glass coverslip,
AIMR researchers have constructedsmall circuits of rat neurons in a dish1.
This allowed them to mimic the way
neurons are connected in the brain,
revealing important insights into themysterious field of brain dynamics.
The human brain is made up of specialized regions that process signals from different sources. For example, one region of
the brain processes the colors our eyes see,while another region processes language.
But in addition to this segregationof activities, processed signals fromthe different brain regions need to be
integrated. Evidence of this integration is found in that fact that the brain
recognizes the words red and blue more
quickly if they are written as red andblue than if they are written as red andblue, explains Hideaki Yamamoto of the
AIMR at Tohoku University.
“Generally speaking, integration iswhen different neuronal groups activate
coherently, whereas segregation is a state
where the neuronal groups activate independently,” says Yamamoto. “These twostates of neural activation are well balanced in the brain and underpin its ability
to carry out complex computation.”
But it has not been clear how thebrain coordinates these very different
activities. “The neural basis of information processing in the brain is one of thebiggest challenges in modern naturalscience,” notes Yamamoto.
Now, Yamamoto, working withresearchers at Tohoku University,
the University of Barcelona, Tohoku
Fukushi University, Waseda University
and Yamagata University, has used abottom-up approach to explore thisAIMResearch 2019© 2019 Hideaki Yamamoto

A simple model of the brain consisting of four circuits of rat neurons reveals how
the brain strikes the right balance between two processing strategies

By varying the degree of physical coupling between four modules made up of circuits of rat neurons, AIMR
researchers have mimicked the activity pattern that occurs in actual brains.

problem. Specifically, they created avery simple model of a brain by linking
four modules made up of circuits of rat
neurons. The researchers then investigated how they integrate when theyvaried the degree of physical coupling
between them (see image).
The team discovered that segregationand integration coexist only when there
is almost no coupling between the four
modules. If the coupling is any stronger,
then integration predominates, whereas
the modules operate independently ofeach other if it is weaker.
“By introducing modular organization to in vitro neuronal networks, we
succeeded in suppressing excessive
coherence between the networks and realized activity patterns that more closely

resemble those observed in actual brains,”
says Ayumi Hirano-Iwata of the AIMR,
who led the group. “While the observed
dynamics are still far from the complexity
in brains, we were able to gain insight into
the fundamental mechanisms that shapebrain dynamics.”
In addition to demonstrating theadvantages bestowed by the modularorganization of the brain, the findings illustrate the power of using biophysical approaches to explore collective phenomena
in complex systems.
1. Yamamoto, H., Moriya, S., Ide, K., Hayakawa, T.,
Akima, H., Sato, S., Kubota, S., Tanii, T., Niwano,M., Teller, S. et al. Impact of modular organization
on dynamical richness in cortical networks.
Science Advances 4, eaau4914 (2018).

5

RESEARCH HIGHLIGHTS

Crystal structure:

Fourth crystallographic phase
uncoveredA previously unknown crystallographic
phase has been discovered in ceramic metaloxides by a team of AIMR researchers1.
This adds to the three other known phases
and promises to lead to the developmentof new functional devices.
Not so long ago, solids were classified
as either crystalline, with well-ordered,periodic structures, or amorphous, whichlack any order. This neat, two-way classification scheme was disrupted by Dan
Shechtman’s discovery of quasicrystals in
1984, for which he was awarded the Nobel
Prize in Chemistry in 2011. As their namesuggests, quasicrystals are neither crystalline nor amorphous — they possess longrange order but are not periodic.
Now, with their discovery of a fourth
crystallographic phase, Yuichi Ikuhara
and his colleagues from the AIMR at
Tohoku University have shown that the
picture is more complicated yet.
The team discovered the new phase inthin films of two metal oxides, magnesium oxide (MgO) and neodymium oxide(Nd2O3), by using atomic-resolution
scanning transmission electron micro­
scopy. They subsequently confirmed it byperforming theoretical calculations.
The researchers found the new crystallographic phase in samples made up of
many small crystals of the metal oxides.
Specifically, it occurred at the boundaries
between two or more neighboring crystals. At these locations, the atoms have arandom arrangement in two dimensions
but possess translational symmetry in thethird dimension, meaning that shifting thestructure by a certain amount in that direction causes it to overlap with its original
configuration (see image). Because of thisone-dimensional (1D) order, Ikuhara’s teamrefers to the phase as a 1D-ordered crystal.

6

Reprinted by permission from Springer Nature; Ref. 1 © 2019

A new crystallographic phase found in metal oxides will force crystallographers to
update their classification system for materials

The new crystallographic phase has a random arrangement in one plane, but translation symmetry along thedirection perpendicular to the plane.

“It came as a surprise to us because nosuch structure had been reported for a
simple oxide crystal such as magnesiumoxide, which was thought to be either
crystalline or amorphous,” Ikuhara, theteam leader, says.
This new crystallographic phase is morethan a scientific curiosity — it alters theproperties of the material. For example,
crystalline magnesium oxide is an electrical insulator, but Ikuhara’s team foundthat the 1D-ordered crystals of magnesium oxide are semiconducting. Ikuhara
expects it will be possible to manipulate
other material properties. “It should bepossible to make ceramics less brittle, if
we can fabricate bulk 1D-ordered crystals,” he predicts.
The team has plans to further investigate the crystallographic phase.
“We will study the mechanism bywhich 1D-ordered crystals form,”
Ikuhara explains. “We also want to findout how to make larger 1D-ordered
crystals in order to fabricate novel
functional devices.”
1. Yin, D., Chen, C., Saito, M., Inoue, K. & Ikuhara, Y.
Ceramic phases with one-dimensional long-rangeorder. Nature Materials 18, 19–23 (2019).

AIMResearch 2019

RESEARCH HIGHLIGHTS

Spintronics:

Magnetic tunnel junctions go
ferrimagnetic
A nano-thin layer of manganese is used to fabricate a magnetic tunnel junction
with a high potential for magnetic storage devices

AIMResearch 2019

A

Electrode

B

CoFeB

Reprinted, with permission, from Ref. 1. Copyright (2019) American Chemical Society.

A solid-state structure that is promising
for realizing extremely fast magnetic
storage devices with ultralow power consumptions has been fabricated by AIMR
researchers1.
A magnetic tunnel junction consists of
two magnetic layers separated by a nonmagnetic, insulating layer. Information
can be stored and erased by switching therelative magnetization of the two layers,which is usually done by an electric current flowing through the junction.
A faster, more efficient way to switch
magnetization would be to vary the magnetic anisotropy, that is, the variation ofmagnetic properties of the structure withthe direction of an applied magnetic field.
Ideally, the magnetic anisotropy would becontrolled by an electric voltage, but it has
been difficult to find materials that exhibit
voltage-controlled magnetic anisotropy.
Research efforts to date have focusedon magnetic tunnel junctions based on
ferromagnetic cobalt iron boron (CoFeB),
but since ferromagnetic materials tend to
generate large stray magnetic fields, theycannot be used to fabricate high-density
integrated storage devices.
Now, Kazuya Suzuki of the AIMR at
Tohoku University and his colleagues
have used a new ferrimagnet, which
generates negligible stray fields, to realizea magnetic tunnel junction that exhibits
voltage-controlled magnetic anisotropy.
They achieved this by including a verythin layer of manganese grown on cobalt
gallium (CoGa) in the junction. Althoughmanganese is anti-ferromagnetic or paramagnetic in bulk, their studies had shownthat a nanolayer grown on cobalt gallium
would be ferrimagnetic and possess perpendicular magnetic anisotropy.
The junction fabricated by Suzuki andGa term.

MgO

Mn

CoGa
2nm

2nm

A transmission electron microcopy image (A) and a high-angle annular dark-field scanning transmission electron
microscopy image (B) of the cross-section of the junction.

co-workers included a manganese nanolayer grown on a cobalt gallium seed layer
and capped by a magnesium oxide tunnel
barrier and a magnetic cobalt–iron–boron layer (see image). Measurementsof the electrical resistance through thestructure when a magnetic field was applied parallel and perpendicular to thejunction indicated that the manganesenanolayer possesses a large perpendicularmagnetic anisotropy. Furthermore, theshape of resistance curves varied with theapplied voltage. This shows that the structure exhibits voltage-controlled magnetic
anisotropy, which is very likely due to theelectric-field modulation of the electronic
structure at the interface between the
manganese and magnesium oxide.

The results could open a new line ofresearch in magnetic tunnel junctions.
“This concept might be widely used
for other manganese-based nanolayers,” says Suzuki. “We will do further
research into other non-ferromagnetic
manganese-based materials that convert
to a perpendicular magnetized nanolayer.
This research and concept will promote
the development of new perpendicularmagnetic materials for future spintronicstorage devices.”
1. Suzuki, K. Z., Kimura, S., Kubota, H. & Mizukami,
S. Magnetic tunnel junctions with a nearly zero
moment manganese nanolayer with perpendicularmagnetic anisotropy. ACS Applied Materials &Interfaces 10, 43305–43310 (2018).

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RESEARCH HIGHLIGHTS

Lithium batteries:

Electrode boosts storage capacity

A strong, porous material developed
by AIMR researchers has the potential
to dramatically increase the amountof energy lithium batteries can store1,
enabling more time between charging
mobile devices.
Rechargeable lithium-ion batteries
are widely used to power electronic devices and electric vehicles. Lithium ionsstored on their electrodes during charging are subsequently released during
discharging. One of these electrodes,
known as the anode, is typically madefrom graphite, an inexpensive formof carbon that is used in pencil lead.
However, graphite accommodates a
relatively small amount of lithium ions.
Anodes made from lithium metal havea much higher capacity, but they sufferfrom two problems. As lithium moves
in and out of the anode, thin metalwhiskers, called dendrites, start to sprout
from it. The flow of lithium also causes
the anode expand and contract. Both effects rapidly curb the battery’s efficiency,
and can even cause combustion.
A team led by Mingwei Chen of the
AIMR at Tohoku University has now
shown that anodes made from nano­porous graphene doped with nitrogencan host much more lithium thangraphite. The material is also lightweight,
flexible and highly conductive, making it
promising as a battery anode.
The researchers grew the material inside
a porous nickel template, before etching
the metal away. Its porous structure gave
nitrogen-doped graphene an extremely low
density, enabling it to store large amountsof lithium without adding much weight toa battery. Its layered sheets of carbon atoms
were peppered with nitrogen atoms, which
helped to bind lithium.
After infusing the material’s poreswith lithium, the researchers found that8

© 2019 Gang Huang

A porous graphene material can store and release large amounts of lithium

Nanoporous nitrogen-doped graphene contains a very large surface area that helps it to store lithium.

the anode could undergo more than 700
charge–discharge cycles without any
significant loss in performance, morethan four times as many cycles as a purelithium electrode. “I was really surprisedby its ultrahigh stability,” comments Gang
Huang, a member of Chen’s team.
Scanning electron microscope images
revealed that dendrites did not grow on
the anode, and its volume varied little on
charging and discharging.
Furthermore, the charge storage capacity of the anode was a mere 10% lower
than the theoretical maximum capacity ofa pure lithium metal electrode. “The specific capacity of our nanoporous anode isnearly 10 times greater than the graphite
electrodes typically used in lithium-ion
batteries,” notes Huang.
A battery containing the anode hada high charging rate and consistently
outperformed a rival with a pure lithium
anode. The researchers hope to apply
the same anode design to other metalelectrode batteries, such as those using
sodium or magnesium.
1. Huang, G., Han, J., Zhang, F., Wang, Z., Kashani,
H., Watanabe, K. & Chen, M. Lithiophilic 3D
nanoporous nitrogen-doped graphene fordendrite-free and ultrahigh-rate lithium-metal
anodes. Advanced Materials 31, 1805334 (2018).

AIMResearch 2019

RESEARCH HIGHLIGHTS

Lithium batteries:

Complex hydride promising as
solid electrolyte
A designed hydride has a combination of properties that make it nearly ideal as anelectrolyte in all-solid-state lithium batteries

AIMResearch 2019

Lithium superionic
conductivity
Two types ofhydrogen clusters© 2019 Shin-ichi Orimo

A new hydride developed by AIMR
researchers could help finally realize allsolid-state lithium batteries1. This opens
up a new direction for scientists to pursue
in the race to develop better performing
replacements for ubiquitous lithium-ion
batteries.
Lithium-ion batteries are used extensively to power everything from smartphones to electric vehicles. But they cansuffer from several drawbacks, including
low energy densities, leakage of the liquid
electrolyte, and the potential to burst intoflames. All three problems could be overcome by replacing the liquid electrolytewith a solid one.
Lithium metal is the material of choicefor the anodes of such all-solid-statebatteries, but existing solid electrolytes
undergo unwanted side reactions withlithium, which increase the resistance
between the anode and electrolyte. This inturn degrades battery performance after
repeated charging and discharging.
Complex hydrides are inorganic compounds that consist of a positive metal ion
and a molecular anion that contains hydrogen. While they do not undergo side
reactions with lithium, they suffer from a
low lithium ion conductivity.
Now, Sangryun Kim of the Institutefor Materials Research (IMR) at Tohoku
University, together with IMR and AIMR
colleagues, has developed a complex hydride that combines both a high lithium
conductivity and a good stability withlithium metal anodes, such that they do
not react with them.
“This is the first time that complex
hydrides have been shown to be suitable
solid electrolytes for practical lithiummetal batteries,” notes Kim. “To oursurprise, we found that the resistanceHigh stability with lithium anode
A complex hydride that has two types of hydrogen clusters exhibits both a high lithium ion conductivity and an
excellent stability with lithium metal anodes.

between our complex hydride and alithium metal anode was almost negligible, meaning that lithium ions can freely
move between the anode and electrolytewith scarcely any barrier.”
The researchers developed the complex
hydride by tailoring the structures of its
hydrogen clusters. The complex hydrideconsists of a mixture of two types of anions (see image): 70% of anions containone carbon atom and nine boron atoms(as in (CB9H10)−), while 30% contain one
carbon atom and eleven boron atoms (asin (CB11H12)−).
“This material is a totally new kind ofsolid electrolyte,” says Kim. “We hope ourresults will inspire future efforts to findlithium superionic conductors based oncomplex hydrides and also open up a new

trend in solid electrolyte materials, which
may lead to the development of highenergy-density electrochemical devices.”
The team intends to further improvetheir electrolyte. “There are many othercomplex anions that we can investigate,”
comments Kim. “Taking the present workas the first step, we intend to conduct
systematic studies to produce complex
hydrides that have even better lithium ion
conductivity and stability with lithium
metal anodes.”1. Kim, S., Oguchi, H., Toyama, N., Sato, T., Takagi,S., Otomo, T., Arunkumar, D., Kuwata, N.,
Kawamura, J. & Orimo, S. A complex hydride
lithium superionic conductor for high-energydensity all-solid-state lithium metal batteries.
Nature Communications 10, 1081 (2019).

9

RESEARCH HIGHLIGHTS

Topological phases:

Two new fermions discovered

Two new fermions have been found in a
topological material by AIMR researchers1.
This is remarkable because, unlike ‘quasiparticle’ fermions previously discovered inmaterial systems, these two quasiparticle
fermions lack particle counterparts thatcan exist in a vacuum.
Particles with an integer spin areclassified as bosons, whereas particles
with a half-integer spin are called
fermions. The best known example ofa fermion is the electron, which has aspin of one half.
According to quantum field theory,fermions in a vacuum can be further
classified into three types: Dirac, Weyl
or Majorana fermions. Of these, only
Dirac fermions have been observed
as particles in high-energy physics
experiments performed at massive
particle accelerators such as CERN’s
Large Hadron Collider. But Dirac andWeyl fermions also been found as quasiparticles — collective excitations ofelectrons that behave as particles — intopological materials, exotic systems
whose surface properties differ greatly
from their bulk properties.
Now, Takafumi Sato of the AIMR at
Tohoku University and his co-workers
have found two new fermion quasiparticles that do not fit into any of thethree categories. They discovered these
fermions in cobalt silicide (CoSi) by usingsynchrotron radiation to probe the energy
levels of electrons in the material.
“Our discovery is exciting because it adds
a new category of fermionic quasiparticles tothe well-known Dirac and Weyl fermions,”
explains Sato. “We anticipate it will stimulate
the search for new types of fermionic quasiparticles in a wider variety of topologicalmaterials using synchrotron radiation.”10

Reprinted, with permission, from Ref. 1 © 2019 by the American Physical Society

Two fermions have been found that can exist only as quasiparticles
inside topological crystals

An angle-resolved photoemission spectrum that reveals the existence of one of the two new kinds of fermions
discovered in cobalt silicide.

The researchers were inspired tosearch for the fermions by a theoreticalprediction published two years ago thatmaterials such as cobalt silicide with achiral crystal structure will harbor suchfermions. The specific point-group symmetry of these crystals permits them tohost fermions that cannot exist in thehigher symmetry of free space.
Sato notes that it was challenging toprepare samples of CoSi that were clean
and flat enough to analyze. “We cleaved
millimeter-sized bulk CoSi crystals morethan 50 times,” he recalls. “In just a few
cases, we were able to obtain a sufficiently
flat surface in a very narrow region of
about 100 by 100 micrometers.”

The discovery could lead to practicalapplications in the future. “While it’s still
early days, this finding could pave the way
toward realizing next-generation electronic devices that utilize new fermions,” notes
Sato. “They may be useful for high-speed
devices because nodal fermions generally
have high mobilities, and their chirality
might make them applicable to some optoand magneto-electronic devices.”
1. Takane, D., Wang, Z., Souma, S., Nakayama, K.,
Nakamura, T., Oinuma, H., Nakata, Y., Iwasawa,
H., Cacho, C., Kim, T. et al. Observation of chiralfermions with a large topological charge andassociated Fermi-arc surface states in CoSi.
Physical Review Letters 122, 076402 (2019).

AIMResearch 2019

RESEARCH HIGHLIGHTS

Nanoporous graphene:High strength and flexibility
achieved
An ultralight, graphene-based material that is both extremely strong andductile has been developed by AIMR
researchers1. These properties makethe material promising for a wide range
of applications, including those in theaerospace and automotive industries.
Graphene’s strength is well documented — the flat sheet of carbon atoms arranged in a hexagonal honeycomb lattice
is one of the strongest materials discovered to date, hundreds of times stronger
than steel. But it has been challenging to
use graphene’s two-dimensional strength
to form strong three-dimensional structures, particularly those that can withstand tension (forces that seek to pull
the structures apart), because graphene’s
strength is reduced if it contains any
defects. In addition, adjacent graphenesheets are held together by weak Vander-Waal bonds.
Furthermore, it has been difficult to realize lightweight, carbon-based materials
that are both strong and ductile.
Now, inspired by the structures ofrecently developed artificial materials known as metamaterials, Hamzeh
Kashani and Mingwei Chen of the AIMRat Tohoku University and their colleagues
have made an ultralight graphene structure containing nanoscale pores that has
an excellent tensile strength and ductility.
“Metamaterials are artificially engineered structures on the microscaleor nanoscale whose unique properties
stem mainly from their structure rather
than the properties of their constituent
materials,” says Kashani. “By using thisconcept and employing a bicontinuous,
nanoscale architecture, we were able toshape a single sheet of graphene into athree-dimensional structure.”

AIMResearch 2019

Reprinted with permission of AAAS from Ref. 1. © Kashani et al., some rights reserved;
exclusive licensee American Association for the Advancement of Science. Distributed under aCreative Commons Attribution NonCommercial License 4.0 (CC BY-NC)

Excellent tensile strength and ductility have been realized in an ultralight,
three-dimensional structure made of nanoporous graphene

This nanoporous, graphene-based structure has both high tensile strength and ductility.

The team produced centimeter-sizedpieces of the material by growing graphene on a nickel block that contained
nanosized pores. They then stripped away
the nickel by etching, so that only a threedimensional seamless tubular network ofgraphene remained (see image).
The secret to the material’s simultaneous strength and flexibility lies in the factthat the graphene structural elements canboth stretch with an extremely high inplane strength and bend with out-of-plane
flexibility. “Lightweight porous structuresthat deform with stretching-dominatedmodes show higher strength and stiffness,whereas those with bending-dominatedmodes have lower strength and stiffness
but offer more flexibility and ductility,” explains Kashani. “Our material can

respond to loads in entirely new ways
through a combination of stretching andbending deformation modes.”The results have broader implications
for two-dimensional materials besides
graphene. “Our work demonstrates thatthe two-dimensional properties of materials can be exploited by judicious designof the architecture of three-dimensional
nanostructures,” says Kashani.
The team now intends to improve the physical and mechanical properties of composite
materials by using their graphene material toreinforce metal and polymer matrices.
1. Kashani, H., Ito, Y., Han, J., Liu, P. & Chen, M.
Extraordinary tensile strength and ductility of
scalable nanoporous graphene. Science Advances
5, eaat6951 (2019).

11

RESEARCH HIGHLIGHTS

Topological insulators:

Imaging nanoscale domains on amultilayer structure
The mosaic surface of a multilayer
structure made up of two materials withdifferent topological properties has been
imaged at a nanoscale resolution by
AIMR researchers1. As well as providing
important insights into the heterostructure, their results demonstrate the powerof the nanoscale-resolution spectroscopy
technique they used.
Exotic materials known as topologicalinsulators have been attracting a lot ofinterest since their discovery a decadeago. Because of their topological properties, electric currents can flow on theirsurfaces but not inside them.
While blocks or thin films of topological insulators have been the main
focus of research, structures made up ofalternating layers of topological insulatorsand other materials are beginning to be
explored. They have the advantage that
their properties can be tuned by varying
parameters like the thickness and stacking sequence of the layers.
“Such wide tunability is very usefulfor realizing novel topological phenomena,” notes Takafumi Sato of the AIMR at
Tohoku University. “For example, inserting
superconducting or magnetic layers into acrystal may realize topological superconductivity or the magnetoelectric effect,
respectively.”
One useful technique for examining how
the structural parameters of such multilayered structures affect the electrical properties of their surfaces is angle-resolved
photoemission spectroscopy (ARPES).
However, the beam of a conventional
ARPES system is far too large to resolve thenanoscale variation in surface properties.
To overcome this, Sato and his
co-workers at Tohoku University’s
Department of Physics and elsewhere12© 2019 Takafumi Sato

A nanoscale beam allowed the surface of a multilayer topological structure
to be imaged for the first time

By using angle-resolved photoemission spectroscopy (ARPES) with a nanoscale beam (red ‘pencil’ on left),
researchers at AIMR were able to image the domains on a multilayer topological heterostructure and determine
their electronic states (blue ARPES intensity plot).

used a nano-ARPES system that has abeam size of about 120 nanometers —more than 800 times smaller than thatof a conventional system — to probe thesurface of a topological heterostructure
made up of layers of lead selenide, a normal insulator alternating with layers ofbismuth selenide, a topological insulator.
They were able to directly observe
nanoscale domains on the surface of theheterostructure and determine their size,
shape and distribution. Furthermore, theresearchers could determine the electronic
state of each domain and find out how thedomains varied with the thickness of the
topological insulator layers within a sample.
To conduct their experiments, theresearchers traveled to France to use oneof only about three nano-ARPES systems
in the world. But in a few years they will
be able to use a new synchrotron that isbeing constructed at Tohoku University.
And by using an even higher resolution
nano-ARPES system, they hope to be able
to resolve the boundary between different
domains, which may host topologicaledge states that exhibit peculiar properties. “Nobody has ever observed this edge
state directly by ARPES,” says Sato.
1. Nakayama, K., Souma, S., Trang, C. X., Takane,
D., Chen, C., Avila, J., Takahashi, T., Sasaki, S.,
Segawa, K., Asensio, M. C. et al. Nanomosaic
of topological Dirac states on the surface of
Pb5Bi24Se41 observed by nano-ARPES. Nano
Letters 19, 3737–3742 (2019).

AIMResearch 2019

RESEARCH HIGHLIGHTS

Electrochemical water splitting:Mathematically designed
graphene on edge
Mathematically optimized graphenebased structures containing the rightcombination of nitrogen and phosphorus
atoms could match — or even outperform— expensive platinum catalysts for producing hydrogen, an AIMR co-led teamhas shown1. This could make hydrogenproduction cheaper and thereby facilitate
the widespread adoption of hydrogen inplace of fossil fuels.
Platinum is currently the material of
choice for catalyzing the hydrogen evolution reaction (HER). In this process,renewable electricity from solar panels or
wind turbines is used to electrolyze water,
releasing clean hydrogen, which can be
stored, transported and used as a fuel.
When hydrogen is burned, water vapor isthe only emission.
However, because platinum is rare,electrocatalysts made from cheap,
abundant carbon — in the form of singleatom-thick sheets called graphene — arebeing investigated. Graphene’s HER activity is affected by various factors, including
chemical dopants and atomic defect structures such as those around holes in thegraphene sheet, says Akichika Kumataniof the AIMR at Tohoku University.
“However, there’s no direct evidence as
to which factors — atomic structures,chemical dopants or both — give thehighest performance,” he explains.
To answer that question, the researchers
designed atomic structures of graphenemathematically and then produced thestructures using chemical vapor deposition
with silicon dioxide nanoparticles. They
also developed scanning electrochemicalcell microscopy (SECCM) for characterizing the graphene structures. It essentiallyenabled them to recreate an electrochemical cell inside a scanning microscope, so

AIMResearch 2019

© ANIMATE4.COM/SCIENCE PHOTO LIBARY

Holey sheets of chemically doped graphene have great potential
for generating clean hydrogen fuelIntroducing defects and chemical dopants can boost the electrocatalytic activity of graphene for the hydrogen
evolution reaction.

that they could measure the HER at different points across the graphene surface witha high spatial resolution.
Using SECCM, the team comparedthe HER performance of graphene withand without holes, and with and without
nitrogen and phosphorus dopant atoms.
They found that the most catalytically
active sites were areas of doped graphenearound the edges of holes. The graphenearound the holes has the greatest concentration of defects in the carbon lattice,which can accommodate many dopant
atoms in close proximity.
Computational studies gave further
insights. The most catalytically active
sites were nitrogen atoms in a ‘pyridinic’bonding arrangement with surrounding
carbon atoms, especially if they were colocated with phosphorus atoms, which
enhanced the charge on the pyridinic nitrogen, further boosting catalytic activity.

"Remarkably, our theoretical results
suggested that the optimal structurebeats platinum’s performance for waterelectrolysis," Kumatani says. "Importantly,
the atom structure was inspired by mathematical analysis. We believe this carbonbased structure for HER can be essential
for developing a sustainable hydrogen
economy."The team plans to optimize methods
for creating graphene with more holey
edges with chemical dopants, as well as
to use SECCM to study other importantelectrochemical reactions such as carbon
dioxide reduction.
1. Kumatani, A., Miura, C., Kuramochi, H., Ohto, T.,
Wakisaka, M., Nagata, Y., Ida, H., Takahashi, Y.,
Hu, K., Jeong, S. et al. Chemical dopants on edgeof holey graphene accelerate electrochemicalhydrogen evolution reaction. Advanced Science 6,1900119 (2019).

13

RESEARCH HIGHLIGHTS

Magnetic materials:

A magnet that can twist and turn
Liquid droplets containing nanoparticles can have permanent magnetism

15s

2mm
Three liquid droplets that have a permanent magnetization can be made to rotate in unison by applying a rotating magnetic field. The orange dye shows the swirling fluid
flow created by the rotating droplets.

A liquid that is a permanent magnet has
been developed for the first time by an
AIMR-led team1. In the future, it could
be used for various applications, such as
actuators in liquid robotic systems.
Liquids that become magnetic whenplaced inside a magnetic field have been
known since the 1960s, when NASA scientists investigated their potential use as
rocket fuel. However, as soon as the magnetic field is switched off, these liquids
rapidly lose their magnetism due to thethermal motion of magnetic particles.
Until now, the only known permanent
magnets were solids.
Now, Tom Russell of the AIMRat Tohoku University and his collaborators in the USA and China havesucceeded in making small liquid
droplets that behave similarly to solid
permanent magnets, but retain liquidcharacteristics.
The team used a modified threedimensional printer to inject millimeter-sized water droplets containing
iron oxide nanoparticles into an oil

14

containing a surfactant. The nanoparticles congregated near the surfaces of thedroplets, forming shell-like structures.
When a magnetic field was applied, thenanoparticles became magnetized. But
to the team’s surprise, the droplets retained some of this magnetization evenwhen the magnetic field was turned off.
The researchers demonstrated theirliquid magnets in various ways. For example, they made several of them rotate
in unison by applying a rotating magnetic field (see image). Furthermore,by drawing a spherical droplet into a
narrow tube so that it became cylindrical, the team showed that the dropletsremained magnetic even on changing
their shape. The magnetization remained even when a droplet was broken
up into hundreds of smaller droplets,
effectively forming multiple permanent
magnets.
The magnetic droplets are much
more than a scientific curiosity; they
have various exciting applications.
“Conventional solid magnets have madegreat contributions to the developmentof modern industry,” says Russell. “Butwhat if magnets were soft, flowable andreconfigurable like a liquid? Magnets
that could conform to spatial constraints? The reconfigurable ferromagnetic liquid droplets we have uncovered
represent a milestone for the further development of magnetic materials. These
amazing liquid magnetic materials will
attract attention in biology, physics andchemistry.”
Since the researchers are uncertain
about how their liquid retains its magnetism, discovering the mechanism is amajor priority. “We do not understandthe exact coupling since the length scales
between the particles is too large for
dipolar coupling,” says Russell. “And so
we’re currently investigating the exact
origin of the coupling.”
1. Liu, X., Kent, N., Ceballos, A., Streubel, R.,
Jiang, Y., Chai, Y., Kim, P. Y., Forth, J., Hellman,
F., Shi, S. et al. Reconfigurable ferromagnetic
liquid droplets. Science 365, 264−267 (2019).

AIMResearch 2019

From Ref. 1. Reprinted with permission from AAAS.

0s

RESEARCH HIGHLIGHTS

Metallic glasses:

Discovering better
combinations faster
A rapid approach for making and testing
metallic glasses has been developed by
AIMR researchers1. This method promises to greatly speed up the search for
optimized metallic glasses.
First discovered in 1960, metallic glasses
are metal alloys that have an amorphous,glass-like structure rather than a crystalline structure like conventional alloys.
They have many useful properties, including high processability, high strength, andresistance to wear and corrosion.
For metallic glasses to be useful for applications such as electronic components
and biomedical implants they need tomaintain this glass-like state over a wide
temperature range. “Generally, metallic
glass with a wide supercooled liquid region
can be fabricated into large samples andeasily shaped into different structures,
which is good for commercial applications,” explains Zhen Lu of the AIMR at
Tohoku University. They also need a highglass-transition temperature — the point
at which they change from a glass to asupercooled liquid — to ensure that they
have a good thermal stability and a highstiffness. However, finding metallic glasses
that satisfy these two criteria through trial
and error is painstakingly slow.
Now, Lu and collaborators at theInstitute of Physics (Chinese Academy of
Sciences) and other institutions in China
and the United States have come up witha fast method for making and measuring
metallic alloys made up of different proportions of three metals, and have used it
to find a metallic glass with a high glasstransition temperature of 1,162 kelvin.
The team sputtered three metals —iridium, nickel and tantalum — onto asubstrate, the proportions of which varied
continuously with position on the substrate.

AIMResearch 2019

Reprinted by permission from Nature: (Ref. 1), copyright (2019).

A new and powerful method for accelerating the optimization of metallic glasses
has been demonstrated

The mechanical properties of metallic glasses make them suitable for small components such as microgears.

They then measured the electrical resistivity
at different points on the substrate. As resistivity correlates to glass-forming ability, theresearchers were able to quickly and easily
identify regions where metallic glasses had
formed. They also tested the mechanicalproperties at different substrate locations.
“By combining a high-throughput fabrication method such as magnetron co-sputteringwith high-throughput measurements, we can
explore a library of samples containing hundreds of components and properties in just a
few days,” says Lu. “This approach promises
to greatly accelerate the development rate andextend the exploration range of new materials.”
The method is straightforward
to implement. “Unlike previous approaches, it can be directly used for many

glass-forming systems,” says Lu. “It costs
about US$3,000 to build the apparatus
we used for mapping electrical resistance,
making it feasible and affordable formany laboratories that lack access to asynchrotron.”
The team wants to apply their method
to other metal combinations. “We plan to
use these high-throughput combinatorial
methods to explore new libraries of metallic glasses and extend the applicationsof metallic glasses,” says Lu.
1. Li, M.-X., Zhao, S.-F., Lu, Z., Hirata, A., Wen, P.,
Bai, H.-Y., Chen, M., Schroers, J. Liu, Y. & Wang,
W.-H. High-temperature bulk metallic glasses
developed by combinatorial methods. Nature 569,
99–103 (2019).

15

RESEARCH HIGHLIGHTS

Fuel-cell catalysts:

Surpassing platinum

A new class of platinum-free catalysts that
could lead to cheaper fuel cells has been
designed by researchers at the AIMR1.
These catalysts have catalytic activities
that surpass those of even ones containing platinum, and can be produced under
mild conditions at low cost.
Hydrogen fuel cells, which generate
electricity by reacting hydrogen and oxygen to produce water, are highly attractive
clean power sources for electric vehicles
and domestic appliances. But one obstacle
for their commercial adoption has been
the fact that the most effective catalysts
for the oxygen-splitting reaction that
occurs on their cathodes are expensive
because they contain the precious metal
platinum. The same problem arises inmetal–air batteries.
With a view to reducing the cost of fuelcells, material scientists have been searching for stable platinum-free catalysts thathave high catalytic activities.
Now, Hiroshi Yabu and Hiroya Abe at the
AIMR at Tohoku University and their coworkers have developed catalysts that tick
all the boxes — they are made from lowcost materials, are easy to make, have a highcatalytic activity, and show good stability.
The team made the catalysts by coating
multiwalled carbon nanotubes with asingle layer of molecules of iron azaphthalocyanines, complexes consisting of aniron atom surrounded by four interconnected aromatic rings.
The researchers had not expected theircatalysts to be as effective. “We were surprised that we could realize a catalytic activity superior to that of platinum-based
catalysts by just swapping the peripheral
benzene groups of phthalocyanine withpyridine groups and adsorbing thiscompound on carbon nanotubes,” notes
Yabu. “Indeed, as far as we’re aware,
this is the highest activity obtained for16

© 2019 Hiroshi Yabu and Hiroya Abe

Inexpensive catalysts can exceed the performance of those containing platinum

A schematic drawing showing the atomic structure of a new catalyst whose catalytic activity is higher than thatof platinum-containing catalysts (gray spheres: carbon atoms in carbon nanotubes; yellow spheres: iron atoms;
blue spheres: nitrogen atoms; white atoms: carbon atoms in azaphthalocyanine rings; red spheres: oxygen atoms;
green spheres: hydrogen atoms).

conventional catalysts based on modified
carbon nanotubes.” The researchers foundthat this high activity is due to the favorable positioning of nitrogen atoms in theazaphthalocyanine rings.
The catalysts have the added advantage
that, unlike other platinum-free catalysts,
they do not require high temperatures
to manufacture. “Our phthalocyanine
derivative dissolves in organic solventsand is easily absorbed onto the carbon
nanotubes,” says Yabu. “This is a great advantage compared with catalysts made bypyrolysis, which require complex, hightemperature processes and good controlof the process conditions.”
The team has established a newcompany to supply the catalysts
worldwide. Furthermore, they are
performing theoretical calculations
to try to find other phthalocyanine
derivatives that have even higher
catalytic activities. “We believe thiskind of collaboration, involving boththeory and experiment, will lead tothe development of many more highly
functional materials,” says Yabu.
1. Abe, H., Hirai, Y., Ikeda, S., Matsuo, Y.,
Matsuyama, H., Nakamura, J., Matsue, T. & Yabu,
H. Fe azaphthalocyanine unimolecular layers (FeAzULs) on carbon nanotubes for realizing highly
active oxygen reduction reaction (ORR) catalyticelectrodes. NPG Asia Materials 11, 57 (2019).

AIMResearch 2019

RESEARCH HIGHLIGHTS

Iron-based superconductors:

Ruling out a cause for hightemperature superconductivity
Measurements on a sister system eliminate a popular explanation for the hightemperature superconductivity of iron selenide monolayers

AIMResearch 2019

Sulfur molecular beam

Reproduced from Ref. 1, with permission from PNAS © 2019

Flying in the face of expectations, thehigh-temperature superconductivity ofa single-atomic layer of iron selenide on
strontium titanate cannot be explained
solely by coupling between electrons andsound waves, experimentalists at AIMR
have shown1. This finding will force material scientists to re-evaluate the origin of
the system’s superconductivity.
The system consisting of a monolayerof iron selenide (FeSe) on a strontium
titanate (SrTiO3) substrate caused a stir in2012 when it was found to superconduct
at the high temperature of 65 kelvin, making it the iron-based superconductor withthe highest transition temperature.
It is also anomalous in that almost all
high-temperature superconductors lose
their high-temperature superconductivity when they are made into monolayer
films, whereas the transition temperatureof iron selenide actually increases from
8 kelvin for a block of the material to 65
kelvin for a single-atom layer.
There has been a lot of discussion about
what is responsible for the superconductivity of monolayer iron selenide on
strontium titanate. A popular explanationis that coupling between electrons in themonolayer and sound waves (phonons)in the substrate alone generates thesuperconductivity.
Now, by performing measurements ona sister system to iron selenide, Takafumi
Sato at the AIMR at Tohoku University,
Kosuke Nakayama at Tohoku University,and their co-workers, have demonstrated
that this mechanism can be ruled out.
They did this by growing a single-atomfilm of iron sulphide (FeS) on strontium
titanate and revealing that, while it had
the same crystal structure as iron selenide
and strong electron–phonon coupling,

S
Fe

Te
Fe

Topotactic reaction

Takafumi Sato and his team produced a monolayer of iron sulphide for the first time by using molecular-beam
epitaxy to deposit sulfur atoms on a monolayer of iron telluride (left image) and then inducing a topotactic
reaction to replace the tellurium atoms in the monolayer with sulfur atoms.

it did not exhibit high-temperature
superconductivity.
This finding came as a surprise to
the team. “We were so sure that electron–phonon coupling was essential forhigh-temperature superconductivity iniron selenide that when we observed it inmonolayer iron sulphide we felt almost
certain that we had made a new high-temperature superconductor,” recalls Sato. He
notes that while the measurement showsthat electron–phonon coupling is not
solely responsible for the superconductivity, the coupling may still contribute to it.
Until now no-one had succeeded in
growing a monolayer of iron sulphide. To
achieve that, the team developed a new
fabrication method that involved first
depositing sulfur atoms on a monolayerof iron telluride (see image). They then induced a reaction that effectively swapped
the tellurium atoms with sulfur atoms.
This fabrication method is promising formaking other novel functional materials
such as metal dichalcogenides and topological systems.
The team suspects that strong correlations between electrons in the ironselenide monolayer may be responsiblefor its superconductivity, and they are
now doing experiments to test this hunch.
1. Shigekawa, K., Nakayama, K., Kuno, M., Phan,
G. N., Owada, K., Sugawara, K., Takahashi, T.
& Sato, T. Dichotomy of superconductivity
between monolayer FeS and FeSe. Proceedingsof the National Academy of Sciences USA 116,
24470–24474 (2019).

17

IN THE SPOTLIGHT

IN THE SPOTLIGHT
The AIMR has grown rapidly since its inauguration in 2007. It now boasts about 100 leading researchers from allover
the world, including 25 internationally renowned principal investigators who are charged withPublishedpioneering
online on 00 Month 2019
XXXX
new and innovative breakthroughs in materials science. The institute is also active in developing young, promisingresearchers with a focus on strong cross-disciplinary collaboration and creativity. AIMResearch spotlights thesetalented researchers of the present and future, detailing their daily research activities and scientific ambitions.

Xxxxxx xxxxx xxxxxxx xxxx
xxxx xxxxxxxx xxxxxxx
xxxx xxxxxxxxx

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AIMResearch 2019

IN THE SPOTLIGHT

INTERNATIONAL SYMPOSIUM

Published online on 25 March 2019

Seeking synergies between fields
and countries
A gathering of innovative scientists sparked lively discussions on the future of materials science and spintronics

Over 250 researchers attended the three-day symposium.

Tohoku University’s selection as a
Designated National University by
the Japanese government in 2017is spurring efforts to build up world-classresearch capabilities in four of its strongest
fields: materials science, spintronics,
next-generation medical care, and disasterscience. As a continuation of the inaugural2018 symposium that celebrated new
beginnings in two of these fields, materials science and spintronics, the Second
Symposium for World Leading ResearchCenters was held in Sendai on 16–18
February 2019.
The meeting gave more than 250
researchers from Japan and around the

AIMResearch 2019

world a valuable opportunity to exchange
ideas about topics as wide ranging as
structural materials, electronic materials,
biomaterials, energy materials, mathematics and informatics. A recurring themeof the symposium was the importance ofcollaboration that transcends disciplinary
and national borders.
The importance of multidisciplinary,collaborative research
In his opening remarks, Hideo Ohno, arenowned physicist and the president of
Tohoku University, noted that many ofhistory’s greatest scientific achievements
were realized through collaboration. By

way of example, he described Tohoku
University’s outstanding contributions in
the field of magnetism, from the pioneering work of Kotaro Honda more than acentury ago to Masato Sagawa’s recent
invention of the strongest magnets. Ohno
expressed his hope that collaborative efforts between disciplines will continue tobuild on such successes.
Motoko Kotani, director of the AIMRat the time, shared further examples of theuniversity’s breakthroughs in materials research, computer science and engineering.
She explained how Tohoku University isadopting a multilayer approach to establish an ecosystem designed to strengthen19IN THE SPOTLIGHT

research activities not only at the newmaterials science center but also across theuniversity’s core research clusters.
“More than 400 researchers are now
working on materials science at Tohoku
University,” she said. “And synergy is
the key to building successful interdisciplinary research alliances with a
global reach.”
As the leader of the spintronics
research center, Yoshiro Hirayama, professor at Tohoku University’s Departmentof Physics, explained how activities at
the Center for Science and Innovation in
Spintronics and its core research clusterare “laying technological foundations fornext-generation Internet of Things (IoT)
applications.” He also spoke of the key
partnership between Tohoku University
and Tsinghua University as a springboard
for more developments in spintronics andtopological materials.
Qi-Kun Xue, a professor and vicepresident of Tsinghua University inBeijing, China, and a principal investigatorat the AIMR, stressed the importance ofmaterials science and spintronics research
for realizing sustainable development. The
close collaborations between Tsinghua
University and Tohoku University nurtured over more than 20 years, he said, willcontinue to encourage joint research inthese critical fields.
From glazed pottery to ultrafast
memory devices
The first of two plenary speakers was Alan
Lindsay Greer, a professor of materials
science at the University of Cambridge
and a long-time collaborator and principal
investigator at the AIMR. He outlined
developments in crystallization studies on
different kinds of glass-forming systems
such as polymers, chalcogenides, metals
and alloys. Greer described a remarkablerange of crystal growth rates correlatedwith thermodynamic and kinetic parameters — of fundamental interest as well asof potential importance for developing ultrafast computing systems. “Studies of fast
crystallization are relevant for computer
memory, and may point to the application

Alan Lindsay Greer talks about the potential of studying the crystallization of various glass-forming systems.

20

of metals for fast phase change,” he said.
Greer then reflected on the question ofwhether pure metals could be considered
glass formers, despite previous assumptions to the contrary. “It seems we can,and this may even be exploitable,” he said,
describing the concept of liquid fragility,and how a possible crossover from fragile
to strong liquid behavior on cooling
could be a vital part of understanding
fast crystal growth. “The ancients knew
about this property of glasses, as it turns
out to be highly relevant to glass blowing,”
Greer noted. “And this fragile-to-strong
crossover may be important for the performance of memory devices.”
Sharing images of nineteenth-century
glazed pottery from France and Japan,
Greer gave other examples of what canbe achieved by phase transformation.
The ring patterns in these artworks, heexplained, indicate where the potter haschanged the temperature of the furnace,
and are subject to a considerable degreeof control. Greer drew parallels between
these patterns and the nanoscale spiralpatterns produced by an intriguing phenomenon known as explosive crystallization in amorphous thin films. Much still
remains to be explored, Greer suggested,in designing and optimizing materials forphase-change applications.
The next step for quantum computing
In a talk titled ‘Why should we care about
topological quantum computer?’, Kang
Wang of the University of California, Los
Angeles, spoke about the exciting possibilities that would be opened up by quantum computing devices to solve problems
that go far beyond the limits of classicalcomputers. There is great potential in drug
discovery, techniques for analyzing thewhole body, smart traffic management,
earthquake disaster prevention, and eventhe ability to count the number of atoms in
the observable universe.
Today’s computers are based on abinary system that uses zeros and ones andoperates in a sequential mode. In contrast,
quantum computers “offer a drasticallydifferent way of computing in massive
parallelism using quantum bits (qubits),
which are superimposed or entangled,
such that one and zero can no longer beconsidered independent states,” Wang
explained. “However, the superpositionand entanglement need to maintain phase

AIMResearch 2019

IN THE SPOTLIGHT

coherence, which is the key challenge forrealizing quantum computing and scaling
up the number of qubits.”
Wang described how his group has
discovered a new direction for realizing
robust topological quantum computingthat overcomes the challenge of decoherence. They have found firm evidence forthe existence of the elusive Majorana
fermion — a particle that is its own antiparticle, which was theoretically predicted
by Ettore Majorana in 1937. “Majorana
particles could be used as topological qubits to realize robust topological quantum
computing,” Wang said.
Interdisciplinary research andeducation united by mathematical
approaches
The symposium’s seven sessions included
two additions this year: a session onmathematics and informatics chairedby Hiroshi Suito, a principal investigatorat the AIMR, and another on Tohoku
University’s new Graduate Programin Materials Science (GP-MS), led by
Katsunari Oikawa, a professor at theGraduate School of Engineering. GP-MS
officially launches in April 2019, andit joins a growing list of international
double-degree programs that includes the
Graduate Program in Spintronics (GPSpin) and the Graduate Program in Data
Science (GP-DS).
The addition of this mathematics andinformatics session reflects the growingrole that mathematics and its applications
play in a data-rich world. “At the AIMR,
one of our unique strengths is our ability to investigate materials science underpinned by mathematics,” said Kotani. “Andin today’s digitalized society, we are seeing
the rise of artificial intelligence, IoT and
big data. More and more researchers, notjust at the AIMR but around the world, areinterested in extending mathematical ideas
to these areas. The new session is a good
opportunity to showcase what we can do.”Mathematics is a universal languagethat cuts across traditional disciplines,
Kotani said. Commenting on AIMR’s
allure for the world’s top minds, she
expressed her hope that more women
will be inspired to consider researchpaths and careers in mathematics andmaterials sciences.
The three-day symposium, which
covered a wide range of fields, was highly

AIMResearch 2019

Kang Wang is excited about the potential of quantum computing.

The poster session gave researchers the opportunity to discuss their latest discoveries.

successful in promoting multidisciplinary
research and international collaboration,
thanks to the attendance of collaboratorsand friends from around the world. It provided a forum for lively discussions about
the cutting edge of materials science andspintronics — two fields which the AIMR
has been focusing on since its foundation.
A more specialist workshop on glasses

had been held as a satellite event a dayprior to the symposium. First held in2012 to promote collaboration between
the fields of mathematics and materials
science, this workshop has been held every
year subsequently. It gave participants
more opportunities for in-depth discussions about metallic glasses and otheramorphous materials. n

21IN THE SPOTLIGHT

INTERNATIONAL WORKSHOPS

Published online on 27 July 2019

Promoting interaction between
material scientists in Europe
and Japan
Two recent meetings in France provided AIMR researchers a unique opportunity to both share
their latest results and strengthen ties with European scientistsTwo major events in the materials
science calendar are the Springand Fall Meetings of the European
Materials Research Society (E-MRS).
With a view to enhancing awarenessof the Advanced Institute for Materials
Research (AIMR) beyond Japan, members from the institute participatedin this year’s E-MRS Spring Meeting,which was held on 27–31 May 2019. It
was organized in conjunction with theInternational Conference on Advanced
Materials (ICAM) of the International
Union of Materials Research Societies(IUMRS). As a result of AIMR’s long
relationship with E-MRS and strong
participation in previous meetings, former AIMR director, Motoko Kotani, was
one of the five conference chairpersons
at this year’s spring meeting.
Like in 2014, 2016 and 2018, AIMR
joined forces with representatives
from the three other materials-related
World Premier International ResearchCenter Initiative (WPI) centers, namely
the International Center for Materials
Nanoarchitectonics (MANA), the Institutefor Integrated Cell-Material Sciences(iCeMS) and the International Institutefor Carbon-Neutral Energy Research(I2CNER), to promote the WPI in Europe
and beyond during this major international conference. A few days after the
E-MRS Spring Meeting, the representatives of the four centers jointly participatedin NanoMat, a workshop designed tostrengthen partnerships between nanomaterials researchers in France and Japan.
Combining forces to promotematerials science in Europe
As in past years, the four WPI centers ran
an exhibition booth at the 2019 E-MRS

22

Staff at the World Premier International Research Center Initiative (WPI) exhibition booth at the 2019 E-MRS
Spring Meeting interacting with visitors.

Spring Meeting to introduce the activities
of WPI and the four centers. The booth,which ran for three days (28–30 May),

displayed posters and brochures about
the WPI project and the four WPI
centers. In addition, visitors had the

AIMResearch 2019

IN THE SPOTLIGHT

Left: Hiroshi Yabu discusses using metafluids to strongly enhance molecular sensing at the 2019 E-MRS Spring Meeting. Right: Teng Ma (wearing a white shirt) at the 2019
E-MRS Spring Meeting explaining his poster on improving the stability and performance of perovskite photovoltaics.

chance to win various prizes in a lottery.
Outreach staff from the four WPI centersanswered questions and described thecenters’ unique research environments
and significant achievements. The booth
attracted researchers from a diverse rangeof fields and countries, including bothsenior scientists, many of whom hadcollaborated with Japanese researchers or
had stayed in Japan, and young researchers, many of whom were interested in
exploring opportunities for advancing
their careers at institutions in Japan.
In the scientific sessions, AIMR researchers gave two oral and four poster
presentations. Hiroshi Yabu talked
about a new class of materials known
as metafluids that respond to magnetic
fields and that can be used to strongly
enhance the sensing of molecules byan analytic technique known as Raman
spectroscopy, and Akichika Kumatani
discussed analyzing graphite and graphene using a scanning electrochemical

AIMResearch 2019

cell microscope. In the poster session,
Teng Ma introduced his poster on optimizing the lateral structure of materials
known as perovskites to realize stable
and highly efficient solar cells. His proposal for simultaneously improving thestability and performance of perovskite
photovoltaics won the best poster award.
The state of the art in sensors
Immediately after the main E-MRS Spring
Meeting, a joint France–Japan workshop
on molecular technology for advanced
sensors was held as a satellite event. After
introductions by Anne Charrier of theCenter for Interdisciplinary Nanoscienceof Marseille and Yutaka Wakayama, deputy director of MANA, ten invited speakers
presented their latest results on a wide
range of sensor technologies, including
sensors for detecting molecules, gas, lightand biomaterials, sensors that use organic
field-effect transistors, sensors based onpolymers and organic compounds, andsensors that employ electrical, electrochemical and optical transduction. From
AIMR, Kumatani talked about nanoscale
electrochemical imaging of electrodematerials using a scanning electrochemical cell microscope. He proposed a new
approach for designing two-dimensional
materials, such as graphene, that is basedon mathematical output, and he confirmed
their high electrochemical performanceexperimentally by microscopic imaging.
His presentation generated a lot of interest,
as evidenced by the ensuing discussions.
The long relationship between France andJapan in materials science seems set tocontinue to promote the development of
cutting-edge sensor technologies.
Exploring nanomaterials together
After the E-MRS Spring Meeting, theNanoMat 2019 Workshop was held on
3–5 June 2019 at the Jussieu campus ofSorbonne University in Paris. It has been
held alternately in France and Japan. This23

IN THE SPOTLIGHT

Akichika Kumatani discussing the nanoscale electrochemical imaging at NanoMat 2019.

year it combined the 13th Japan–FranceWorkshop on Nanomaterials and thefourth WPI Workshop on Materials
Science. This meeting was co-organized by
the French CNRS National Competency
Cluster in Nanoscience (C’Nano) and
MANA, iCeMS, I2CNER and AIMR.
The workshop started with welcome
speeches by Corinne Chaneac, director
of C’Nano and the main organizer of thisyear’s workshop, and Stéphane Régnier,dean of the Faculty of Science andEngineering, Sorbonne University. After
that, representatives of the four WPI centers, Tomonobu Nakayama from MANA,
Hiroshige Matsumoto from I 2CNER,

24

Susumu Ikeda from AIMR and Mitsuru
Hashida from iCeMS, introduced theirrespective centers. French and Japanese
researchers then gave scientific oralpresentations. In the evening, Ma, Ikeda
and Hiroya Abe from AIMR presented
posters, which all resulted in fruitful
discussions with French scientists. On
the second day of NanoMat 2019, Yabu
talked about synthesizing nanocomposite
materials and Kumatani spoke aboutnanoscale electrochemical imaging
on lithium-ion battery electrodes. The
meeting included in a facility tour, one
highlight of which was a laboratory containing nearly all of the nuclear magnetic

resonance (NMR) systems at the Jussieu
campus of Sorbonne University.
During the workshop, it was announced that the next NanoMat workshop will be hosted by AIMR in Sendai.
This opportunity promises to further
strengthen the good relationship in materials science between France and Japan.
These two latest events in France
have further raised awareness of AIMR
in France and Europe. By participatingin future scientific exchange events,
including the next NanoMat workshop,
AIMR intends to forge even stronger
cooperative ties with researchers
overseas. n

AIMResearch 2019

AIMResearch
AIMResearch is an online and print publication that highlights the scientific achievements and activities of
the AIMR. First published in June 2009, AIMResearch selects the most important papers from the wealthof research produced by AIMR scientists throughout the year, distilling the essence of the achievements
into timely, concise and accessible research highlights that are easy to digest, but retain all of the impact andimportance of the original research article. Published monthly on the AIMResearch website in both English
and Japanese, AIMResearch research highlights bring the very best of AIMR research to a global audience ofspecialists and nonspecialists alike. AIMResearch also publishes a range of feature articles introducing otheractivities of the AIMR’s research groups. Visitors to the website can register for monthly email alerts in either
English or Japanese to keep abreast of the latest developments and discoveries made at the AIMR.
wpi-aimr.tohoku.ac.jp/en/aimresearch/

wpi-aimr.tohoku.ac.jp/en/aimresearch/
AIMResearch is published by the Advanced Institute for Materials Research (AIMR)at Tohoku University in collaboration with the Partnership and Custom Media unitof Nature Research, a division of Nature Japan KK.
© 2020 AIMR, Tohoku University. This publication may be reproduced in its
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Editorial
AIMR, Tohoku University
2-1-1 Katahira, Aoba-ku, Sendai,
Miyagi 980-8577, Japan
Editor-in-Chief

Shin-ichi Orimo

Managing Editor

Takashi Takahashi

Editorial AssistantEtsuko Hagita

ISSN 1884-491X

Advanced Institute for Materials Research
Tohoku University