is a parallel supercomputer with relatively loose coupling.
It consists of 19 nodes inter-connected by a gigabit Ethernet
network. Each node is a distributed-shared-memory- typecomputer consisting of 64 Intel Itanium 2 CPUs interconnected by a rather high performance network and have 64
GB memory. System B archives 7.7 TFlops total throughput
performance.
All staff member of university faculties or public research
institutes in Japan are invited to propose research projects(called User Program). The proposals are evaluated by theSteering Committee of SCC. Pre-reviewing is done by theSupercomputer Project Advisory Committee. In school year
2008 totally 181 projects were approved. The total points
applied and approved are listed on Table. 1 below.
The research projects are roughly classified into thefollowing three (the number of projects approved):

Highlights of Joint Research
Synchrotron Radiation Laboratory
The Synchrotron Radiation Laboratory (SRL) wasestablished in 1975 as a research group dedicating to solidstate physics using synchrotron radiation. In 1989, the SRL
started to hold the Tsukuba branch, a branch laboratory in
the Photon Factory (PF), High Energy Accelerator Research
Organization (KEK). The SRL consists of the accelerator
physics group and the solid state spectroscopy group. The
members of the accelerator group have been carrying out
research works on the accelerator physics and developing
various new accelerator related technology in collaboration with other SR facilities. The spectroscopy group has
been not only serving users at the Tsukuba branch withtechnical supports and advices, but also carrying out theirown research works on advanced solid state spectroscopy.
SRL maintains an undulator called Revolver, two beamlines
and three experimental stations; BL-18A for angle-resolved
photoemission spectroscopy with SCIENTA SES100 energy
analyser and undulator beamlines, BL-19A and BL-19B,
for spin-resolved photoelectron spectroscopy and soft X-ray
emission spectroscopy experiments, respectively. In 2008,
the new spin detector utilizing very low energy electron
diffraction (VLEED) has started its normal operation. They
are fully opened to outside users for experiments using highbrilliant synchrotron radiation from the undulator. The operation time of these beamlines are about 4000 hours and thenumber of users is more than 100 a year.
The staff members of SRL, the solid state spectroscopy group participate to the Materials Research Divisionof the Synchrotron Radiation Research Organization of
the University of Tokyo (SRRO). They play essential roles
in promoting scientific activities using SR and started toconstruct a new 25m-long undulator and beamline at theSPring-8, BL07-LSU. The beamline is equipped with experimental apparatuses using high brilliance synchrotron radia-

Fig. 1. The horizontal figure-8 undulators installed in SPring-8

30

ISSP Activity Report 2008

tion in soft X-ray region. They are those for time-resolved
experiments and nano-materials research experiments, which
will only be possible using third generation light source
and will promise us a considerable progress in the studies
of nano-particles and real time observation of magnetic
domains and of chemical reaction at catalytic surfaces, etc.
They will be available in October in 2009.
The accelerator group performed the detailed design ofthe new 25-m undulator of the University of Tokyo in collaboration with the SPring-8 ID and accelerator groups. The
four horizontal figure-8 undulator segments were alreadyconstructed and installed with a good alignment error in thelong straight section of SPring-8. Field measurements of aphase shifter prototype started to be used in examining its
performance. The accelerator group also studied future ERL(energy recovery linac) light sources and developed ERL
components such as superconducting cavities and fiber laser
oscillators for driving an ERL photocathode gun in collaboration with KEK, AIST and JAEA.

Neutron Science Laboratory
The Neutron Science Laboratory (NSL) has been playing
a central role in neutron scattering activities in Japan since
1961 by performing its own research programs as well as
providing a strong general user program for the universityowned various neutron scattering spectrometers installedat the JRR-3 operated by Japan Atomic Energy Agency inTokai. In 2003, the Neutron Scattering Laboratory was
reorganized as the Neutron Science Laboratory to further
promote the neutron science with use of the instruments in
JRR-3. Under the general user program supported by NSL,
14 university-group-owned spectrometers in the JRR-3
reactor (20MW) are available for a wide scope of researches
on material science, and proposals close to 300 are submitted
each year, and the number of visiting users under thisprogram reaches over 6000 person-day/year.
Triple axis spectrometers and a high resolution powder
diffractometer are utilized for a conventional solid statephysics and a variety of research fields on hard-condensed
matter, while in the field of soft-condensed matter science,researches are mostly carried out by using the small angle
neutron scattering (SANS-U) and/or neutron spin echo
(iNSE) instruments. The upgraded time-of-flight (TOF)
inelastic scattering spectrometer is also available through the
ISSP-NSL user program.
Major research topics on the hard-condensed matterscience cover stripe order in high-Tc superconductors, andclosely related 2 dimensional systems, charge and orbital

First-Principles Calculation of Materials Properties (67)
Strongly Correlated Quantum Systems (40)
Cooperative Phenomena in Complex, Macroscopic
Systems (75)Fig. 1. The reactor hall of JRR-3. The eight neutron scattering instruments are attached to the horizontal beam tubes in the reactor experimental hall. Two thermal and three cold guides are extracted from thereactor core towards the guide hall located to the left.

ordering in CMR manganites, quadrapolar ordering inrare-earth based intermetallic compounds, spin dynamics oflow dimensional dimmer systems, etc. On the other hand, theresearch topics on the soft-condensed matter science cover
structural characterization of polymer gels, polymer blends,
micelles, amphiphilic polymers, block copolymers, proteins,
dynamics of brush-polymers on surface, slow dynamics ofsurfactants, pressure dependence of dynamics of amphiphilic membranes, and so on. In addition, there are a varietyof activities on fundamental physics, neutron beam optics,
developments of neutron scattering techniques.
The NSL also operates the U.S.-Japan cooperative
program on neutron scattering, providing further research
opportunities to material scientists who utilize the neutron
scattering technique for their research interests.
The details of individual studies and research highlights
in JFY2008 are reported in the NSL-ISSP Activity Report
vol. 15. (http://quasi.issp.u-tokyo.ac.jp/actrep/actrep-15/
index-pub_vol15.html).

All the three involve both methodology of computationand its applications. The results of the projects are reported
in 'Activity Report 2008' of the SCC. Everyyear typicallyfour projects are selected for “invited papers” and publishedat the beggining of the Activity Report. In the Activity
Report 2008, the following four invited papers are included:“Vector spin chirality and multiferroic properties in
one-dimensional spin-1/2 frustrated magnets”, by
Shunsuke FURUKAWA, Masahiro SATO, Yasuhiro
SAIGA, and Shigeki ONODA“Jammed vortex matter” by Hajime YOSHINO, Tomoaki
NOGAWA, Bongsoo KIM, and Hikaru KAWAMURA“Chemical reaction dynamics accompanying electrontransfer”by Osamu SUGINOClass Max/Min

Application

PointsNumberof
Projects

Supercomputer Center
The Supercomputer Center (SCC) is a part of theMaterials Design and Characterization Laboratory (MDCL)of ISSP. Its mission is to serve the whole community ofcomputational condensed-matter physics of Japan providing
it with high performance computing environment. In particular, the SCC selectively promotes and supports large-scalecomputations. For this purpose, the SCC invites proposals forsupercomputer-aided research projects and hosts the Steering
Committee, as mentioned below, to evaluate the proposals.
The SCC operates two super-computers, systems A and
B. System A is Hitachi SR11000/48 that consists of 48 highperformance nodes composed of tightly- coupled microprocessors. With the aid of the automatic parallelization of
FORTRAN compiler, a node of System A can be used as if
it were a single-processor computer. System A has 2.8TB
memory and archives 5.8 TFlops peak performance in total.
On the other hand, System B, which is SGI Altix 3700/1280,

Total Points
AppliedApproved

System A

System B

System A

System B

A<100K

any time

2

150K

50K

150K

50K

B

<2M

twice a year

43

47M

36M

39M

32M

C

<20M

twice a year

127

1200M

930M

1046M

851M

any time

9

175M

155M

173M

145M

D
S
Total

>20M

twice a year

0

0M

0M

0M

0M

181

1422M

1121M

1258M

1028M

Table 1. Research projects approved in 2008. The maximum points
allotted to the project of each class are the sum of the points for the twosystems; 1 K point of System-A corresponds to charge for 0.37 hours
× node, while the corresponding figure is 0.22 hours × 64CPU for
System-B.

ISSP Activity Report 200831

International MegaGauss
Science Laboratory
The aim of this laboratory is to study the physicalproperties of solid-state materials (such as semiconductors,
magnetic materials, metals, insulators, superconducting
materials) under ultra-high magnetic field conditions. Sucha high magnetic field is also used for controlling the newmaterial phase and functions. Our pulse magnets, at moment,
can generate up to 85 Tesla by non-destructive manner, andfrom 100 up to 730 Tesla (the world strongest as an in-door
record) by destructive (the single turn coil and the electromagnetic flux compression) methods.
They are opened for scientists both from Japan and fromoverseas, especially from Asian countries, and many fruitfulresults are expected to come out not only from collaborative research but also from our in-house activities. One of
our ultimate goals is to provide the scientific users as our
joint research with magnets capable of a 100 T, milli-second
pulses in a non-destructive mode, and to offer versatile
physical precision measurements. The available measuring
techniques now involve magneto-optical measurements,
cyclotron resonance, spin resonance, magnetization andtransport measurements.
Our interests cover the study on quantum phase transitions (QPT) induced by high magnetic fields. Field-induced
QPT has been explored in various materials such as quantum
spin systems, strongly correlated electron systems and othermagnetic materials. Non-destructive strong pulse magnets
are expected to provide us with reliable and precise solidstate physics measurements. The number of collaborative groups for the research is over 50 in the year of 2007.
Multiple extreme physical conditions combined withultra-low temperatures and ultra-high pressures are alsoavailable.
A 210 MJ flywheel generator which is the world largest
DC power supply (recorded in Guinness book of records in
1997/98) has been installed in the newly built DC Flywheel
generator station at our Institute. The generator, once disas-sembled from the one used for Toroidal magnetic field coilin JFT-2M (JAERI Fusion Torus-2M) Tokamak nuclear
fusion testing device, is now renewed as a power supply forthe pulse magnets. The construction of the magnet service
station has also been accomplished. The magnet technologies
are intensively devoted to the quasi-steady long pulse magnet(an order of 1-10 sec) energized by the giant DC power
supply, and also used for the outer-magnet coil to realize a
100 Tesla nondestructive magnet.
Our destructive magnets, such as the single-turn coil andthe electro-magnetic flux compression (EMFC) systems,
would be oriented toward easier access and more reliablemeasurements for solid-state physics than previously obtainable. One of our recent successes was the achievement ofover 730 T within a 4 MJ energy injection by the EMFC, inwhich a new type of primary coil with a simpler design was
employed. These are oriented for developing new horizons inmaterial science realized under such extreme quantum limit
conditions.

Enhancement of Optical Second
Harmonic Generation by
Nitrogen Adsorption on Cu(001)
G. Mizutani, N. Kawamura, and F. Komori
Optical second harmonic generation (SHG) is a powerfultool for investigating the electronic states of a solid systembecause it provides information both on occupied andunoccupied electronic states around the Fermi energy [1]. We
have studied SHG from the clean and nitrogen (N) adsorbed
Cu(001) surfaces. This system has attracted interest because
on a partially N-covered Cu(001) surface a well ordered
nano-grid pattern is formed from alternating clean andN-adsorbed surface areas [2]. The observed SHG signal waslargely enhanced by the N adsorption. Surface SH responsesof the Cu(001) surfaces based on electronic states werealso studied using an ab initio approach, and the valence
electronic states are compared with the results of angle
resolved photoemission spectroscopy (ARPES).
Figure 1 shows the experimental results for the incident
polarization angle dependence of the p- and s-polarized
SHG intensity from the N-saturated, N-adsorbed grid, andclean Cu(001) surfaces. The p-polarized SHG intensity has amaximum for the p-polarized incident light for both the clean
and N-adsorbed surfaces. The maximum values both on the
N-saturated and N-adsorbed grid surfaces are 30 times larger
than that on the clean surface. The s-polarized SHG intensity from the clean surface is a minimum for both the p- ands-polarized incident light. The calculated band structure for
the N-saturated surface is consistent with the results of the
ARPES measurement as shown in Fig. 2. The polarization
angle dependence of SHG calculated for the same surface
qualitatively agrees with the experimental observations, andthe enhancement is mainly attributed to the change of theFig. 2. (a) Calculated band structure of the Cu(001)c(2×2)-N surface
along the Γ-X’-M’-Γ path. The filled circles indicate energy states ofpronounced N 2p character, while the open circles correspond to statesassignable to Cu atoms in the topmost and 2nd layer. (b) Experimentally observed N-derived states along the Γ-X’ and Γ-M’ directions by
ARPES are plotted in the same energy and wave vector scale in Fig.
2(a). The gray zone is the d-band area. The inset shows the surface
Brillouin zone of the clean and Cu(001)c(2×2)-N surfaces.

surface electronic states due to the N-adsorption.
On the grid surface, the p-SHG intensity generated by
the p-polarized incident light is almost the same as thaton the N-saturated surface. This is inconsistent with thesimple assumption that the SHG signal originates from theN-covered c(2×2). The N-adsorbed area is 2/3 of the wholesurface. Possible origins of the largely enhanced SHG on thegrid surface are the lattice deformation due to the grid patternformation and the presence of a long interface between theclean Cu surface and the N-adsorbed surface.
References[1] C. Schwaba, G. Meistera, A. Goldmann, and E. Bertel, Surf. Sci.
469, 93 (2000).
[2] F. M. Leibsle, C. F. J. Flipse, and A. W. Robinson, Phys. Rev. B 47,
15865 (1993).
Authors
H. Sanoa, M. Miyaokab, T. Iimori, D. Sekiba, K. Nakatsuji, W. Wolfc,
R. Podlouckyd, N. Kawamurab, G. Mizutania, and F. KomoriaJapan Advanced Institute of Science and Technologyb
NHK Sci./Technical Research Laboratoriesc
Materials DesigndUniversity of Vienna

Oxide Switch
Fig. 1. The building for the flywheel generator (right hand side) anda long pulse magnet station (left hand side). The flywheel giant DC
generator is 350 ton in weight and 5 m high (bottom). The generator,
capable of a 51 mega watt out put power with a 210 mega joule energy
storage, is planned to energize the long pulse magnet generating 100
Tesla without destruction.

32

ISSP Activity Report 2008

Fig. 1. Incident polarization angle dependence of the p- and s-polarized
SHG intensity from the N-saturated (a), N-adsorbed grid (b), and clean(c) Cu(001) surfaces. The second harmonic light was generated by theincident light with a wavelength of 800 nm (1.55 eV). The origin of theincident polarization angle (θ = 0) is p-polarized.

I. Ohkubo and M. Lippmaa
Various oxide thin film-based switching devices havebeen proposed. Non-volatile switching between conducting

ISSP Activity Report 200833

Spin Waves, Vortex Excitations andMagnon BEC of Superfluid 3He-A in
Restricted Geometry, as in Parallel-Plates
and in Oriented Aerogel
Y. Sasaki, O. Ishikawa, and M. Kubota
3

Fig. 1. Structure of the switching devices grown on(LaAlO3)0.3-(Sr2AlTaO6)0.7 (LSAT) substrate. The bottom electrodeis a metallic (La,Sr)MnO 3 layer. Switching occurs either in thePr1-xCaxMnO3 layer or at the top electrode interface. Vertical transport through the heterostructure occurs in micron-scale pillars that areetched into the thin film multilayer, shown in the inset photo.

and non-conducting states can occur under the influence ofelectric field, as in resistive switching, or by some other formof external excitation, such as light illumination or exposure
to a magnetic field. In the present work, the purpose is tofabricate a trilayer oxide thin film device structure that canbe used to measure transport in the perpendicular direction
across a heterointerface as opposed to the more common
planar geometry, in which transport is measured parallel toan active interface, e.g. in a field-effect transistor.
A cross-sectional schematic diagram and a plan-view
photo of a lithographically patterned device are shown in
Fig. 1. The thin film multilayer consisting of (La,Sr)MnO3(LSMO) and Pr1-xCaxMnO3 (PCMO) is fabricated first bypulsed laser deposition, followed by a lithography step andion milling that exposes and forms the shape of the LSMO
bottom electrode. In the second step, the PCMO pillar structure is surrounded by a SiO2 isolation layer and the device isfinished by fabricating top metal electrodes by a lithographic
lift-off process. Each sample contains several tens of pillar
structures with diameters ranging from 5 to 50 µm.
Work is proceeding on characterizing the switchingproperties of these pillar samples. In case the top electrodeis Aluminum, resistive switching occurs at the electrode /PCMO interface, driven by a field-induced formation ofaluminum oxide at the top interface of the PCMO film.
Since the LSMO electrode and PCMO switching layers
are both ferromagnetic oxides, it is also possible to study themagnetic properties of confined oxide microstructures andfollow the transport properties of the magnetic heterostructures under external magnetic fields.

He-A phase is a unique anisotropic superfluid state,composed with p-wave Cooper pairs of 3He atoms. We
present here recent two examples of our study, in which
the orientation axis for d vector, which represents the spincomponent of the Cooper pairs, is made perpendicular to lvector, which represents the orbital angular momentum of
the pair. The first example uses the sample placed between
parallel plates with 12.5 μm gap, where we discuss a newobservation of new satellite signal under rotation andpossible half quantized vortices and Fre’edericksz transition[1]. Whereas the second example uses Aerogel, a very dilute
material with large open space of 98% volume, and withanisotropic orientation of the density gradient, to fill “3He-A
like” phase. We find macroscopic coherent precession ofmagnetization in this phase for the first time. This phenomenon is regarded as a manifest of the magnon Bose Einstein
Condensation (BEC) in the magnetic superfluid 3He-A[2].
Example 1: Quantized vortices with half-integer circulation, which are forbidden from existing in a conventional
superﬂuid because of the single valueness of the wave
function, are theoretically predicted to exist in superﬂuid
3
He-A if the order parameters l and d form l ⊥ d texture.
To form the l ⊥ d texture, we conﬁned the superﬂuid 3He-A
between parallel plates with a 12.5 μm gap and applied amagnetic ﬁeld of H = 26.7 mT perpendicular to the plates
to take NMR and orient d perpendicular to l. NMR spectra
exhibit a negative-shift peak which probes that the uniforml ⊥ d texture is realized in our cell and show a new satellite
signal under rotation. The rotation dependence of the satellite signal is interpreted that a Fre´edericksz transition of l
texture is induced by rotation above 1.0 rad/s and vortices
start to appear above 1.8 rad/s [1].
Figure 1 shows Rotation dependence of normalized sizeof the NMR satellite signal at 0.81 Tc, which indicates atransition, which we interpret as Fre’edericksz transition,
where uniform textural state transforms into a nonuniform

one. Actually, from this signal we analize that singly or halfquantized vorices start to penetrate into the sample from theedge at Ωc. An alternative explanation has been proposed by
H. Y. Kee and K. Maki[3], involving half quantum vortices.
Example 2: We report the ﬁrst observation of coherent
precession of magnetization in superﬂuid 3He A-like phase(CPA) in aerogel [4]. The coherent precession in bulk 3He
A-phase is unstable due to the positive feed-back of spin
supercurrent to the gradient of phase of precession. It waspredicted that the homogeneous precession will be stable if
the orbital momentum of the 3He A-phase can be oriented
along the magnetic ﬁeld. We have succeeded to prepare thisconﬁguration by immersing uni-axially deformed anisotropic aerogel in 3He. The dissipation rate of the coherent
precession states in aerogel is much larger than that in bulk
3
He B-phase. We propose a mechanism of this dissipation.
Actually this macroscopic coherent precession(MCP) is anevidence of BEC of magnons in 3He-A as discussed in [5].
(The Coherent precession in 3He-A is Partially reported in
AR2007b).
References[1] M. Yamashita, K. Izumina, et al., Phys. Rev. Lett. 101, 025302(2008).
[2] T. Sato, T. Kunimatsu, K. Izumina, et al., Phys. Rev. Lett. 101,055301 (2008).
[3] H. Y. Kee and K. Maki, Europhys. Lett. 80, 46003 (2007).
[4] T. Kunimatsu, A. Matsubara, et al., Physica C 468, 605 (2008).
[5] Yu. Bunkov and G. E. Volovik, Phys. Rev. Lett. 98, 265302 (2007)
Authors
M. Yamashitaa, T. Sato, K. Izumina, A. Matsubarab, Y. Sasakib, O.
Ishikawac, T. Takagid, M. Kubota, T. Mizusakia, and Yu. M. BunkoveaKyoto UniversitybResearch Center for Low Temperature and Materials Sciences, Kyoto
UniversitycOsaka City Universityd
Fukui Universitye
MCBT, Institut Ne´el, CNRS/UJF

Pressure-Induced Superconductivity in
Iron-Pnictide Materials
H. Okada, H. Takahashi, and Y. Uwatoko
High pressure studies have been playing a very importantrole for the investigations on the iron-pnictide superconductors, as well as carrier doping through substitution of atoms.
In the earliest stage, applying pressure for optimally doped

References[1] T. Harada et al., Appl. Phys. Lett. 92, 222113 (2008).
[2] K. Tsubouchi et al., Appl. Phys. Lett. 92, 262109 (2008).
[3] I. Ohkubo et al., Mat. Sci. Eng. B 148, 13 (2008).
Authors
I. Ohkubo a , H. Kumigashira a,c , M. Oshima a,c , T. Ohnishi, K.
Tsubouchia, Y. Matsumotob, K. Itakaa,c, T. Haradaa, H. Koinumaa,c,d,and M. Lippmaaa
The University of Tokyob
Materials and Structures Laboratory, Tokyo Institute of Technologyc
CREST, Japan Science and Technology CorporationdNational Institute for Materials Science

34

ISSP Activity Report 2008

Fig. 1. Rotation dependence of normalized size of the NMR satellite
signal at 0.81 Tc . Data taken in the acceleration (deceleration) process
is shown in red ﬁlled (blue open) symbols. The dashed line is a model
calculation based on the assumption that the Fre´edericksz transition
takes place for Ω ≧ ΩFr and vortices start to appear for Ω ≧ Ωc , whereΩFr = 1.0 rad/s, Ωc = 1.8 rad/s. The peak at Ωc changes its height as afunction of T and seems to go to zero at Tc. An alternative explanation
involving half quantized vortices is proposed[3] and further study isneeded to clarify.

Fig. 2. Pressure dependence of the superconducting transition temperature in LaFeAsO1-xFx series. The solid curves are guides to the eye.

Fig. 1. ρ-T curves of LaFeAsO. The dρ/dT curve shows peak value at
T0. At 12GPa, zero resistivity was observed.

Fig. 3. ρ-T curves of SrFe2As2. T0 is defined as the same manner as
LaFeAsO. At 8GPa, zero resistivity was observed.

LaFeAsO1-xFx increased Tc to 43 K, which is the significantly large enhancement of Tc. Successive studies revealed
the pressure-induced superconductivity for the undoped
iron-pnictide materials [1].
Figure 1 shows the ρ(T) curves of LaFeAsO using a cubic
anvil press. The resistivity shows rapid decrease below 150
K, which is related to the structural and magnetic transitions(T0). In the low temperature range, the sudden decrease ofresistivity caused by superconductivity was observed. Tc
increased up to 21 K at 12 GPa, where the zero resistivity
was observed. This pressure-induced superconductivity was
firstly discovered in the 1111 system. The T0, where thedρ/dT curve shows peak value, is suppressed by pressure,while Tc is enhanced with increasing pressure, as shown in
Fig.2. The lightly doped and undoped LaFeAsO1-xFx shows
the comparatively lower maximum Tc than highly doped
materials. This is thought that the lightly doped one is close
to the magnetic phase. From the latest result on CaFeAsF,
the pressure-induced superconductivity was observed above
the pressure, where the T0 was completely suppressed withpressure.
Figure 3 shows the ρ(T) curves of SrFe2As2 using the
cubic anvil press. Like as LaFeAsO, the T0 was suppressedand superconductivity emerged under high pressure [2]. The
zero resisitivy was observed at 8GPa, which was the firstobservation for SrFe2As2, although several pressure-induced
superconductivity has been observed in AFe2As2 (A = Ca, Sr,Ba) system.

ISSP Activity Report 200835

izing process, the inner diameter partly expanded over 2%
when a load of 15.0 ton was applied. The fracture strain of
high-strength materials is usually not great, sometimes lessthan 3 %, therefore the upper pressure limit of the NiCrAlcylinder is at most 4 GPa. Furthermore, a crack was observedin the WC piston after releasing pressure from 4 GPa. The
compression strength is 6 and 4.5 GPa for magnetic andnonmagnetic WCs, respectively. In the present experiment,
we used the nonmagnetic WC, and therefore the appearanceof the crack is not a surprising. To apply further pressure
with this pressure cell, improvements to materials, especiallyfor the piston, are also required as well as an effective sealing
technique and the total design of the pressure cell.

References[1] H.Okada et al., JPSJ 77 113712 (2008).
[2] K.Igawa et al., JPSJ 78 025001 (2009).
Authors
H. Okadaa, H. Takahashia, K. Matsubayashi, and Y. UwatokoaNihon University

Fabrication and Efficiency Evaluation of aHybrid NiCrAl Pressure Cell up to 4 GPa
N. Fujiwara and Y. Uwatoko
Pressure has became increasingly important in the
research on strongly correlated electron systems, because
several 3d-transition-metal oxides, heavy fermion systems,
and organic conducting systems exhibit a variety of phaseswith applied pressure. The phases include charge-ordering(CO), magnetic ordering, paramagnetic metallic, and superconducting (SC) states. In the case of pressure-induced
superconductivity, a spin- or charge-ordering phase often
appears at the lower pressure side on a pressure-temperature(P-T) phase diagram. Coexistence of the ordering stateswith the SC state, or anomalous metallic behavior near
the quantum critical point (QCP), where the ordering state
becomes unstable, is one of the current important topics instrongly correlated electron systems. In these compounds,
some have been precisely investigated using various
techniques under pressure, whereas the others have not. It is
an important factor whether the onset pressure is achieved bya piston-cylinder-type pressure cell. The current borderline
lies around a pressure of 2.7-3.0 GPa. Recently, NiCrAl or
MP35N cylinders have attracted much attention as post-WC
cylinders, because they are nonmagnetic and possess hightensile and yield strengths. In paticular, NiCrAl contains
fewer impurities than MP35N, and is suitable for magnetic
measurements. In the present work, we applied loads up to
15.0 ton to a hybrid NiCrAl pressure cell and investigated thepressure limit and the efficiency.
We used a special press system arranged on the top
flange of variable-temperature insert (VTI)(Fig. 1) [1]. The
length between the top flange and the bottom of the VTI
is 1340 mm. The pressure cell is screwed into the tension
column made of MP35N, and the load is transferred to theFig. 1. Steady-load control system equipped on the top flange ofvariable-temperature insert (VTI). A load is transferred to the pressure
cell via a compression rod. The pressure cell was screwed onto atension column. The load is supported by the tension column, theCuBe sleeve and backup support. These components act as a frame of aconventional press system.

36

ISSP Activity Report 2008

References[1] N. Fujiwara, T. Matsumoto, K. Koyama-Nakazawa, A. Hisada, andY. Uwatoko, Rev. Sci. Instrum. 78 073905 (2007).
[2] G. J. Piermarni, S. Block, J. D. Barnett, and R. A. Forman, J. App.
Phys. 46 2774 (1975).
[3] A. P. Reyes, E. T. Ahrens, R. H. Heffner, P. C. Hammel, and J. D.
Thompson, Rev. Sci. Instrum. 63 3120 (1992).
Authors
N. Fujiwaraa, T. Matsumoto, K. Koyama-Nakazawa, A. Hisadaa, and Y.
UwatokoaKyoto University

Fig. 2. (a) Load dependence of the R1 shift in ruby fluorescence. (b)Relationship between the NQR frequency of Cu2O and the R1 shift.

pressure cell mediated by the inner compression rod. The
tension column, the CuBe sleeve, and the CuBe backup
support act as a frame in a conventional press system. Steadyload control becomes possible owing to feedback fromthe pressure cell, even at low temperatures where pressure
decrease is expected because of contraction of pressure
mediation liquid. In the present VTI, two trimmer capacitors
are equipped near the pressure cell to adjust NQR frequency
and impedance matching. They are connected to tuning
knobs outside the top flange by extension rods and can becontrolled even at low temperatures.
63
Cu(I=3/2)-NQR measurement of Cu 2 O and rubyfluorescence are very useful as means of pressure calibration
because it does not require any sweeps of physical parameters. Ruby fluorescence is often adopted for diamond anvil
cells. The shift of the R1 transition shows a linear relation
with pressure. G. P. Piermarini, et al. measured pressure
up to 19.5 GPa and obtained the fitting curve as P(GPa) =Δ λ/0.365 (nm) [2]. Cu2O is often used for pressure calibration in nuclear magnetic resonance (NMR) because the NQR
frequency also shows a linear relation with applied pressure.
We performed the 63Cu NQR of Cu2O and ruby fluorescence simultaneously using the steady-load control system
mentioned above. Fig. 2 (a) shows load dependence of the
R1 shift. As seen from the figure, the curve tends to bend
downward with increasing load. The trend becomes remarkable when the heavy load is imposed. The bend is attributable to the loss of efficiency during the pressurizing process.
Fig. 2(b) shows relationship between the NQR frequency
and the R1 shift. We obtained the pressure dependence of the
NQR frequency from Fig. 2(b) as ν(MHz) = 26.0 + 0.32P(GPa). The relation is consistent with an early study [3].
For the deformation of the cylinder during pressur-

Development of Electromagnetic Wave
Absorber for Sub-terahertz Regionin ε-type AlxFe2-xO3
M. Nakajima, S. Ohkoshi, and T. Suemoto
Recently, we have been studying the development of
the electromagnetic wave absorber for millimeter wave
in sub-terahertz range. This range is very expected fornext-generation wireless communication. The development of the electromagnetic absorber in higher frequency
region is urgent theme needed for the next-generation
wireless communication. In general, when an electromagnetic wave is irradiated to a ferromagnet, the resonance due
to gyromagnetic effect is caused. This resonance is calleda “natural resonance” (ferromagnetic resonance) (Fig. 1).
The resonance frequency (fr) is proportional to a magnetocrystalline anisotropy field (Ha), which is expressed by fr =(ν / 2π) Ha, where ν is the gyromagnetic ratio. A magnetic
material with a large coercive field (Hc) is expected to showa high-frequency resonance.
The sample ε-Fe2O3 nanoparticles were prepared by animpregnation method based on mesoporous silica nanoparticles. The other samples for x = 0.06, 0.09, 0.21, 0.30,

Fig. 2. The absorption spectra for ε-AlxFe2−xO3 from x = 0 to 0.40
measured by THz time domain spectroscopy.

and 0.40 in ε-AlxFe2-xO3 were prepared by a combination
method between the reverse-micelle and sol-gel techniques.
The average particle sizes of the materials are between 25–50 nm. These nanomagnets have an extremely large Hc
at 300 K of 10.2 kOe, 14.9 kOe, and 22.5 kOe for x = 0.4,
0.21, and 0, respectively. In addition, aluminum is the third
most common atom, the production cost is very economical,
which is very attractive for practical applications.
Terahertz (THz) time domain spectroscopy using
THz pulses emitted by femtosecond laser pulse excitation is powerful tool for investigating the millimeter wave
and far-infrared region. The absorption measurement for
ε-AlxFe2-xO3 was performed at room temperature using
by THz domain spectroscopy. As a THz wave emitter anddetector, a dipole-type and bow-tie type low-temperaturegrown GaAs photoconductive antennas were used, respectively. The absorption spectra of the THz waves were
calculated by the following equation: (Absorption) = −10
log|t(ω)|2 (dB) (t(ω); complex amplitude transmittance). An
absorption of 20 dB indicates that 99 % of the introduced
electromagnetic waves are absorbed, which is the target
value for electromagnetic absorbers from an industrial pointof view.
Figure 2 shows the absorption spectra. The frequencies of
the absorption peaks for x= 0.40, 0.30, 0.21, 0.09, 0.06, and0 were observed at 112, 125, 145,162, 172, and 182 GHz,
respectively (Fig. 2). In the case of a ferromagnetic material
with a uniaxial magnetic anisotropy, the direction of magnetization was restricted around the magnetic easy-axis. Whenan electromagnetic wave is irradiated to a ferromagnetic
material, the magnetization precesses around the easy-axis
and a natural resonance occurs. The fr value is proportional
to the Ha. When the sample consists of randomly oriented
magnetic particles, the Ha value is proportional to Hc. In fact,
the fr value increased as the Hc value increases.
High-performance millimeter wave absorbers composedof a series of ε-AlxFe2-xO3 (0 ≤ x ≤ 0.40) nanomagnets
were developed and investigated by the THz time domain
spectroscopy. These magnetic materials exhibit natural
resonances in the region of 112–182 GHz, which are thehighest frequencies for magnetic materials. Such high natural
resonance frequencies are achieved by the large magnetic
anisotropies of this series.

Fig. 1. Schematic illustration of the natural resonance due to the
gyromagnetic effect. Precession of magnetization (M) around an anisotropy field (Ha) causes electromagnetic wave absorption.

ISSP Activity Report 200837

Reference[1] A. Namai, S. Sakurai, M. Nakajima, T. Suemoto, K. Matsumoto, M.
Goto, S. Sasaki, and S. Ohkoshi, J. Am. Chem. Soc. 131, 1170 (2009).

References[1] E. I. Rashba, Sov. Phys. Sol. St. 2, 1109 (1960); Y. A. Bychkov, andE. I. Rashba, JETP Lett. 39, 78 (1984).
[2] T. Nakagawa, O. Ohgami, Y. Saito, H. Okuyama, M.Nishijima, andT. Aruga, Phys. Rev. B 75 155409 (2007).
[3] C. R. Ast, J. Henk, A. Ernst, L.Moreschini, M. C. Falub, D.Pacilé,P. Bruno, K. Kern, and M.Grioni, Phys. Rev. Lett. 98 186807 (2007).
[4] S. Hatta, T. Aruga, C. Kato, S. Takahashi, H. Okuyama,
A. Harasawa, T. Okuda, and T. Kinoshita, Phys. Rev. B 77, 245436(2008).
[5] M. Nagano, A Kodama, T. ShiShidou, and T. Oguchi, J. Phys.:
Condens. Matter 21, 064239 (2009).

Authors
M. Nakajima, A. Namaia, S. Sakuraia, S. Ohkoshia, and T. Suemotoa
The University of Tokyo

Rashba Spin splitting of Surface States on
Tl/Ge(111)-(3×1)

Authors
S. Hattaa, T. Okuda*, A. Harasawa, T. Kinoshita**, and T. ArugaaaKyoto University*current address: Hiroshima University** current address: JASRI/SPring-8

S. Hatta and T. Aruga
The spin splitting of two-dimensional (2D) electronic
states due to the Rashba spin–orbit (SO) interaction is
attracting much attention as a key to manipulate electron
spins in solid state [1]. This type of spin splitting is causedby the out-of-plane asymmetry of the electronic potential.
A surface makes such a potential asymmetry, and thus,
intrinsic spin splitting is realized at surfaces. Sizable splittings exceeding ~0.1 eV have been observed on the surfacesof heavy elements such as Au and Bi. The potential of thesehigh-Z nuclei contributes to a strong SO interaction. On
the other hand, the observation of the giant Rashba splitting on Ag surfaces covered with submonolayer Bi [2, 3]
indicates that the surface modification with heavy elements
can enhance the spin splitting on surfaces of lighter elements,
including semiconductors such as Si and Ge.
Here we report on the Rashba spin splitting of the
Tl-induced surface state on the Ge(111) surface [4]. The
Tl/Ge(111)-(31) surface has a quasi-one-dimensional structure, called “honeycomb-chain channel (HCC) structure”,
with Ge adatoms of 4/3 monolayer (ML) and Tl of 1/3 ML.
The HCC structure is commonly found for the other Si(111)and Ge(111) (3×1) surfaces with monovalent metals (alkali
metals and Ag). These surfaces have similar electronic structures identified as the dangling bonds of the Si (Ge) adatoms.
However, the spin splitting of these states has never beenaddressed. We found that the hybridization of the Tl and Ge
orbitals induces large spin splittings on the surface states.
Figure 1 shows the calculated electronic structure of the(3×1) surface. Five surface-related states are found in thebulk band gap around the Fermi level. Using angle-resolved

Fig. 1. Band structure of the Tl/Ge(111)-(3×1) surface calculated withthe full-potential LAPW method. The radii of circles represent thecontribution of the Tl 6p orbitals. The solid curves represent spin-split
bands related to the Ge dangling bonds and Tl. The inset shows the(3×1) surface Brillouin zone.

38

ISSP Activity Report 2008

Quantum Phase Transition in
the 3d Itinerant Antiferromagnet
H. Kadowaki and T. J. Sato
Fig. 2. Charge density plot of (a) S1 and (b) S2 at the A point. (c)Atomic structure of the Tl/Ge(111)-(3×1) surface.

photoelectron spectroscopy with synchrotron radiation at
the ISSP beamline 18A of Photon Factory, we confirmed
the corresponding occupied bands. These bands are split
to pairs of spin-polarized bands respectively. Among them,large spin splittings of 0.1–0.2 eV are found for the S1 andS2 bands, indicated by the blue and red curves, respectively.
The splittings are inhibited at the middle of ΓA and C. The
spin degeneracy at the k points of G/2, where G represents
the 2D reciprocal lattice vector, results from the coupling of
the time-reversal symmetry and the translational symmetry.
In the simple model with the 2D free electrons, the spin splitting shows a linear k dependence as ΔR ∝ 2αRk, where αR iscalled the Rashba parameter. However, the spin splitting on
the (3×1) surface seems to become non-linear at k away fromthe proximity of the degeneracy points. This is partially due
to the change of the orbital hybridization with k.
The orbital analysis of calculated states revealed that thelargely spin-split states have a large contribution of the Tl
6p orbitals, as well as the Ge 4sp-hybridized orbitals. Thisis clearly shown in charge density plots of S1 and S2 at the
A point (Fig. 2). The state of S1 has a dominant danglingbond character of the Ge adatom facing Tl. Moreover, thewavefunction of the spin-split state is spread over a few Ge
layers. On the other hand, the charge distribution of S2 islocalized in the overlayer. Considering the charge density
just around Tl, we found an asymmetry of the p-like distribution, reflecting the hybridization with 6s. According to
an expression of αR ∝ ∫dr(∂V/∂z) |ψ(r)|2 [5], where V is thepotential and ψ(r) the wavefunction, while (∂V/∂z) is approximately odd with respect to the nucleus, the asymmetric
distribution of the wavefunction can lead to a large spin splitting collaborated with the nucleus potential, as observed on
this surface. The hybridization of 6s-6p would be also important for the Rashba spin splitting of surfaces states inducedby other heavy p-block elements such as Pb and Bi.
In conclusion, we have shown that the adsorption of
submonolayer Tl induces the large Rashba spin splitting
on Ge(111). The significant contribution of Tl 6p orbital isshown for the largely spin-split states.

In recent years, novel viewpoints of matter have been
exploited by quantum phase transitions (QPT), zero-temperature second-order phase transitions tuned by pressure orother controlling parameters. Around a QPT, the state ofmatter is characterized by singular behavior of fluctuatingorder parameters having both quantum mechanical andthermal origins. Quantum phase transitions are investigatedin broad fields ranging from high temperature superconductors, metal-insulator transitions, to heavy fermions. Althougha number of QPTs have been investigated experimentallyand theoretically, many problems are under controversial
debates. One of such debates is nature of QPT in itinerant
antiferromagnets (AFM), referred to as the spin density wave(SDW) QPT. Experimentally, thermodynamic and transport properties are in rough agreement with theories of the
SDW QPT. However, most neutron scattering studies seemto contradict expectations of the SDW QPT, exemplified by
the novel E/T scaling of the AFM fluctuations observed in
the heavy fermion CeCu6-xAux, suggesting the existence of a
new type of QPT [1]. In order to terminate the controversy,
in this work we have performed neutron inelastic scattering

Fig. 2. Temperature dependence of the characteristic energy of the AFM
spin fluctuations is plotted as a function of T3/2. The curves represent
the prediction for the SDW QPT and the fit using the SCR theory. The
inset shows temperature dependence of the product χ(Q)Γ(Q).

study onthe prototypical 3d itinerant antiferromagnet(V1-xTix)2O3 (x = 0.1), which is known to be in the proximity
to the QPT separating paramagnetic and antiferromagnetic
metal.
Figure 1 shows results of constant-Q scans at various
temperatures in the paramagnetic region, which areconverted to generalized susceptibility Imχ(Q,ℏω). It was
found that the generalized susceptibility is well approximated by the following Lorentzian function:Imχ(Q+q,ℏω) = χ(Q)Γ(Q)ℏω /{ℏω2 + [Γ(Q) + D(qc2 + Fqab2)]2},
where Q is the AFM modulation vector, ℏω the excitationenergy, qc and qab components of q along c axis and in theab plane. D and F are temperature independent parameters,
whereas χ(Q) and Γ(Q) are the wave-vector-dependent
magnetic susceptibility and characteristic energy. Among
several other predictions, the SDW QCP theory predicts
temperature dependence of the characteristic energy as Γ(Q)= c1 + c2 T3/2. To confirm this prediction, we have plotted
the obtained Γ(Q) parameters at various temperatures versus
T3/2 in Fig. 2. As seen in the figure, the T3/2 behavior was
confirmed up to T = 80 K. This concludes that QPT in this
3d itinerant antiferromagnet is governed by SDW QPT [2].
References[1] S. Sachdev, Quantum Phase Transitions (Cambridge Univ. Press,
Cambridge, 1999).
[2] H. Kadowaki, K. Motoya, T. J. Sato, J. W. Lynn, J. A. FernandezBaca, and J. Kikuchi, Phys. Rev. Lett. 101 096406 (2008) .
Authors
H. Kadowakia, K. Motoyab, T. J. Sato, J. W. Lynnc, J. A. FernandezBacad, and J. KikuchieaTokyo Metropolitan UniversitybTokyo University of Sciencec
NIST Center for Neutron Researchd
Oak Ridge National Laboratorye
Meiji University

Fig. 1. Constant-Q scans measured at the AFM wave vector at several
temperatures. Curves are fit results using Eq. (1). Error bars are statistical in origin and represent 1 standard deviation.

ISSP Activity Report 200839

Quantum Phase Transition in
Two-dimensional Antiferromagnets(CuCl)La(Nb1-xTax)2O7

Jammed Vortex Matter
H. Yoshino and T. Nogawa

H. Kageyama, Y. Ueda, and K. Kindo
Chimie douce offers rational design of the magnetic
lattices in nonmolecular solids. For example, a new class oflayered compounds (CuX)[An-1BnO3n+1] (where X = Cl-, Br-,A = La3+, Ca2+, Na+…, B = Nb5+, Ta5+, Ti4+…, n = 2, 3) has
been obtained by low-temperature ion-exchange reactions[1-6]. As shown in Fig. 1(a), the magnetic CuX layer isseparated well by magnetically inert An-1BnO3n+1 perovskite
slabs, making them good two-dimensional spin-1/2
magnets. Several exotic quantum magnetic phenomena havebeen observed such as collective singlet-ground states in(CuCl)LaNb2O7, collinear order at 32 K in (CuBr)LaNb2O7,
1/3 magnetization plateau in (CuBr)Sr2Nb3O10.
In order to obtain the origin of the spin-singlet formationin (CuCl)LaNb2O7, we investigated the magnetic propertiesof (CuCl)La(Nb1-xTax)2O7 by means of transmission electron
microscopy (TEM), susceptibility, pulsed high-field magnetization, and elastic/inelastic neutron scattering [7]. A crucial
advantage of studying this solid solution is that the magnetic
CuCl plane is preserved and that pentavalent Nb and Ta ionshave almost the same radius (0.64 Å)
The X-ray diffraction patterns of the 0 < x < 1 samples
showed designed synthesis of the solid solution having
nearly the same tetragonal cell parameters as those of(CuCl)LaNb2O7 and (CuCl)LaTa2O7. The TEM experimentsfor (CuCl)LaNb2O7 carried out typically at room temperature using a JEM2010F system with an operating voltage
of 200 kV revealed weak reflections such as (1/2, 0, 0) and(0, 1/2, 0). This indicates the doubling the a- and b-axis [6].
Similar patterns are also obtained for the solid solution. A
uniform distribution of the Nb and Ta atoms is confirmedby the energy-dispersive spectroscopy (EDS) spectrum asshown in Figs. 1 (c), (d).
From the magnetization curves (Fig. 2), it is seen thatthe spin-singlet state is stable up to x ~ 0.4, accompanied bya slight reduction of the spin gap with increasing x. On theFig. 2. Magnetization curves M of (CuCl)La(Nb1-xTax)2O7 at T = 1.3 K.
Inset is an enlarged plot for x = 0, 0.2 and 0.4, highlighting the criticalfields Hc.

Fig. 3. Neutron diffraction profiles of x = 1 around the (1/2, 0, 1/2)
magnetic reflection. Open and closed circles represent the datacollected at 1.7 and 17 K, respectively, and the solid line is a guide to
the eye.

other hand, the neutron diffraction study (Fig. 3) revealed
that (CuCl)LaTa2O7 undergoes, in spite of unaltered cellparameters and preserved CuCl plane, collinear orderwith TN ~ 7 K. In the intermediate region (0.4 < x < 1), we
observed the collinear order with a significantly reduced
magnetic moment but with a nearly constant TN, suggestingthat the collinear order state coexists with the spin-singlet
state.
References[1] H. Kageyama, T. Kitano, N. Oba, M. Nishi, K. Hirota, L. Viciu, J.
B. Wiley, J. Yasuda, Y. Ajiro, and K. Yoshimura, J. Phys. Soc. Jpn. 74,
1702 (2005).
[2] H. Kageyama, J. Yasuda, T. Kitano, K. Totsuka, Y. Narumi, M.
Hagiwara, K. Kindo, Y. Baba, N. Oba, Y. Ajiro, and K. Yoshimura, J.
Phys. Soc. Jpn. 74, 3155 (2005).
[3] A. Kitada, Z. Hiroi, Y. Tsujimoto, T. Kitano, H. Kageyama, Y. Ajiro,
and K. Yoshimura, J. Phys. Soc. Jpn. 76, 093706 (2007).
[4] N. Oba, H. Kageyama, T. Kitano, J. Yasuda, Y. Baba, M. Nishi, K.
Hirota, Y. Narumi, M. Hagiwara, K. Kindo, T. Saito, Y. Ajiro, and K.
Yoshimura, J. Phys. Soc. Jpn. 75, 113601 (2006).
[5] Y. Tsujimoto, Y. Baba, N. Oba, H. Kageyama, T. Fukui, Y. Narumi,
K. Kindo, T. Saito, M. Takano, Y. Ajiro, and K. Yoshimura, J. Phys.
Soc. Jpn. 76, 063711 (2007).
[6] M. Yoshida, N. Ogata, M. Takigawa, J. Yamaura, M. Ichihara, T.
Kitano, and H. Kageyama, J. Phys. Soc. Jpn. 76, 104703 (2007).
[7] A. Kitada et al., submitted to Phys. Rev. B.

Irrationally frustrated Josephson junction array (JJA),
namely JJA with irrational number density of vortexes par
plaquette induced by external magnetic field, is a highly
frustrated system which refuses to be stabilized in simple
periodic manners [1]. The irrational JJA with spatiallyisotropic Josephson coupling on the square lattice is believed
to remain in a vortex liquid state down to zero temperature[2]. However we found strong numerical evidences obtainedby extensive Monte Carlo simulations for static properties
and RCSJ (Resistively and Capacitively Shunted Junction)
simulations for transport properties [3], that even an infinitesimally weak anisotropy of the Josephson coupling into, say x
and y directions induce formation of smectic layers of zigzag
vortex stripes. (Fig. 1)
The vortex pattern is essentially frozen in random zigzag
patterns but the whole frozen-structure can slide into thedirection of stronger coupling due to phason like gapless softmodes. Consequently the system behaves as an unusuallyfragile matter [3]: solid like (non-Ohmic, superconducting)response against external shear on the phase variables (injection of the external electric current) perpendicular to thelayers but liquid like (Ohmic) response against shear parallelto the layers. By the same token, the superconducting
phase coherence remains disordered down to zero temperature, which is analogous to the spin-chirality decoupling
phenomena observed in frustrated magnets [4].
Our motivation to study the anisotropic JJA originatesfrom an unexpected connection to a class of friction modeles
which exhibit the so called Aubry's transition [5] which is a
prototype of jamming transition [6]. We found the current
vs voltage curves exhibit scaling properties similar to thoseof the flow curves (shear-stress vs shear-rate) studied in the
non-linear rheology of granular materials around jamming
point [7]. In the Fig. 2 we summarize our results by showing
the phase diagram of the system. Apparently it is very
similar to the one proposed for the rheology of granular andsoft-glassy systems [6,7].
In Addition to the JJA, we also studied the transport(rheological) properties of the semi-elastic model in which
the sinusoidal coupling in the original JJA model into one

Fig. 2. “Jamming phase diagram” of the irrationally frustrated anisotropic JJA.

direction is replaced by an elastic coupling. The latter modelis presumably closer to the friction model [5]. Indeed wefound the scaling function of the current-voltage curve of
the semi-elastic model is almost indistinguishable fromthe master flow-curve observed in granular systems [7].
Further investigations to clarify relationships among the JJA,
semi-elastic model and the 1-dim friction models [5] will becertainly rewarding.
Whether geometrical frustration alone can realize glassy
phases is a long-standing issue. Halsey [1] has envisionedthat the irrationally frustrated JJA can exhibit a glassy
phase. Our observations suggest the anisotropic irrationally
frustrated JJA realizes floating ziazag stripe glass states.
The intriguing question is whether these 'states' constitutereal thermodynamic glass states. We plan to perform further
investigation to give a definitive answer to this fundamental
question.
References[1] T. C. Halsey, Phys. Rev. Lett. 55, 1018 (1985).
[2] E. Granato, Phys. Rev. Lett. 101, 027004 (2008).
[3] H. Yoshino, T. Nogawa, and B. Kim, New J. Phys. 11, 013010(2009). Movies of the transport dynamics are available in “Supplementary Data”at http://iopscience.iop.org/1367-2630/11/1/013010/[4] S. Teitel and C. Jayaprakash, Phys. Rev. B 27, 598 (1983);
H. Kawamura and M. Tanemura, Phys. Rev. B 36, 7177 (1987).
[5] M. Peyard and S. Aubry, J. Phys. C: Solid State Phys. 16, 1593
(1983); H. Matsukawa and H. Fukuyama, Phys. Rev B. 49, 17286(1994).
[6] Jamming and Rheology, Ed. A. J. Liu , S. R. Nagel, CRC Press(2001).
[7] P. Olsson and S. Teitel, Phys. Rev. Lett. 69, 178001 (2007);
T. Hatano, J. Phys. Soc. Jpn. 77, 123002 (2008); M. Otsuki and
H. Hayakawa, Prog. Theor. Phys. 121, 647 (2009).
Authors
H. Yoshino a, T. Nogawa b, B. Kim c, and H. Kawamura aaOsaka Universityb
The University of Tokyoc
Changwon University

Evidence of Spin Singlet Ground State in the
Frustrated Antiferromagnetic Ring Cr8Ni

Authors
H. Kageyamaa, Y. Ajiroa, K. Yoshimuraa, M. Nishi, Y. Narumi, K.
Kindo, M. Ichihara, and Y. UedaaKyoto University

Y. Furukawa, Y. Narumi, and K. Kindo
Fig. 1. (a) Schematic view of the crystal structure of (CuCl)LaB2O7 (B= Nb, Ta). (b) TEM image and (c), (d) the corresponding EDS mapsof the x = 0.8 sample, where blue and red dots represent Nb and Ta,
respectively.

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ISSP Activity Report 2008

Fig. 1. Smectic zigzag vortex pattern of the irrationally frustrated anisotropic JJA in equilibrium. The blue/white boxes represent presence/
absence of vortexes in the plaquette of the JJA. In this example
Josephson coupling is 1.5 times stronger into the vertical direction than
to the horizontal direction.

Recently there has been intense experimental and theoretical effort in synthesis and investigation of nanoscale molecular magnetic systems, which are composed of a controllable number of transition metal ions [1]. The discovery of

ISSP Activity Report 200841

quantum phenomena [2,3] like quantum tunneling of themagnetization observed in single molecule magnets has
further increased the interest in the investigation of nanoscale
molecular magnets. Among nanoscale molecular magnets are
antiferromagnetic (AF) rings that have an almost coplanarring shape with a number (N) of transition metal ions. A
common feature of all even number rings is to have a spin
singlet ST = 0 ground state due to the dominant AF Heisenberg exchange couplings between nearest neighbor spins.
Due to the finite size effects, AF rings have a discrete energy
spectrum and the lowest-lying magnetic excited states [4].
In the case of odd-number AF rings, magnetic properties
are expected to be changed drastically due to spin frustration.
The simplest systems of odd-number molecular AF rings
are the s = 1/2 three spin system with an AF interaction. In
these frustrated triangular AF spin systems the ground stateis a magnetic ST = 1/2 state [5]. Odd number AF rings with
N > 3 have been more difficult to synthesize. Quite recently abreakthrough in the synthesis of a new family of odd-number
AF rings with N=9 was achieved. A heterometallic Cr-based
ring-shaped AF magnet (C2H11)2NH2{Cr8NiF9[O2CC(CH3)3]18}(abbreviated as, Cr8Ni) was synthesized [6]. As a matter offact, Cr8Ni is the first odd-member AF ring with N > 3. Thissystem has spin frustration effects because all AF interactions cannot be simultaneously satisfied.
The schematic structure of the core of Cr8Ni is shown in
Fig. 1(a). The metal ions are bridged by one fluorine ion andtwo (CH3)3CCO2 radicals [6]. The AF interactions between
the Cr ions and between the Cr and the Ni ions are reported
to be JCr-Cr=16K and JCr-Ni=70K, respectively, from the fitof the temperature dependence of magnetic susceptibility χ
which shows peaks around 2 K and 25 K (see Fig. 1(b)) [6].
From the fitting of the magnetic susceptibility in the temperature range T = 1.6-300 K it is also inferred that the groundstate is a singlet ST = 0 and that the first excited state is a ST
= 1 state at 3.7 K from the ground state. The fit was based ona spin Hamiltonian that included Heisenberg exchange terms
only [6]. The conclusion about the singlet ground state in

Field-Induced Magnetic Phase Transitionsin Multiferroic RbCoBr3.
M. Tokunaga and Y. Nishiwaki

Fig. 2. (a) Magnetization curve of Cr8Ni measured at T = 0.1 K (blacksolid line). Red lines show the theoretical calculated results (dotted line;
without DM interaction, solid line; with DM interaction). (b) dM/dH
curve at T = 0.1 K. Red lines show the theoretical calculated results(dotted line; without DM interaction, solid line; with DM interaction).

this frustrated ring is quite novel and interesting and it thus
requires more direct experimental evidence. In order to elucidate the ground state of the Cr8Ni system from experimental
point of view, it is important to investigate the magnetic
properties at much lower temperature i.e. well below thelowest energy gap. For the purpose, we have carried out highfield magnetization measurements at very low temperatures
down to 0.1 K.
Figure 2(a) shows the magnetization (M) curves for Cr8Ni
at T = 0.1 K for increasing magnetic fields, where a clear
step-wise increase of magnetization is observed. Our experimental results clearly show an evidence of a spin singlet
ground state for the Cr8Ni system and allow us to establish
the energy separation of the low-lying quantum magnetic
states. The experimental results are in good agreement withpredictions from theoretical calculations. Interestingly, thewidth of the steps in the field-dependence of the magnetization show that sizeable Dzyaloshinski-Moriya (DM) interactions are present and lead to anticrossings between states ofdifferent total spin.

Recently, emergence of direct coupling between magnetism and electric polarization in ferroelectric magnets has
attracted considerable attention in condensed-matter physics.
Since magnetic moment (M) and electric polarization (P)have different parity for time-reversal and spatial-inversion
operation, linear combination between the both orderparameters usually does not contribute to the free energy.
Strong coupling between the both is put into reality whensome kinds of spatially modulated spin structures set in. Asa typical example, magnets with cycloidal spin states havebeen the most extensively studied, in which the accompanying P is caused by the anti-symmetric exchange interaction
between the adjacent spins [1,2]. On the other hand, anothermultiferroic state in which symmetric exchange interaction
plays the essential role is less understood although theoretical calculation predicts the presence of the larger P in thismechanism [3].
In this context, we brought our attention to a frustrated
Ising magnet of RbCoBr3. In this material, spins in the Co2+
ions construct quasi-one-dimensional antiferromagnetic
chains along the c-axis. The chains form a triangular lattice
within the ab-plane (see inset of Fig. 1) having antiferromagnetic nearest neighbor interaction. As a consequence of thisfrustration, successive magnetic transitions, i.e. from partial
disorder to ferrimagnetic states, take place with decreasing
temperature [4]. Dielectric measurement revealed that thesemagnetic transitions are accompanied with a significant
change in P [5]. Due to the strong Ising-type anisotropy, thisFig. 1. (a) Schematic view of Cr8Ni. (b) Temperature dependence ofmagnetic susceptibility of Cr8Ni from ref. 6. The solid line shows thetheoretical calculated results.

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ISSP Activity Report 2008

material shows collinear spin ordering, and hence, antisymmetric-type mechanism cannot account for the emergenceof the P. In this study, we studied isothermal magnetization
curves up to 55 T to clarify whether external magnetic fields(H) can modify the spin state that couples with ferroelectricity in this material.
Figure 1(a) shows magnetization curve (blue) and differential susceptibility (dM/dH: red) of RbCoBr3 in H || c-axis
at 4.2 K. In addition to a steep increase in M at around 48 T,
small change in the slope (cusp in the dM/dH) is discernible
at around 38 T as marked by the triangles. The presence of
these anomalies is confirmed by taking systematic temperature variation of the dM/dH curves. As shown in Fig. 1(b),the both anomalies shift to the lower fields as temperature increases. Temperature dependence of the cusp field
is demonstrated in Fig. 2. The both anomalies smoothly
approach the magnetic transition temperatures in zero field.
Thus we derive the phase diagram as described in Fig. 2: theferrimagnetic state at the ground state changes into partial
disorder phase by application of H. Presence of successive
magnetic transitions implies the accompanying change in P.
Further studies on electric polarization are in progress.
References[1] H. Katsura, N. Nagaosa, and A. V. Balatsky, Phys. Rev. Lett. 95,
057205 (2005).
[2] M. Mostovoy, Phys. Rev. Lett. 96, 067601 (2006).
[3] I. A. Sergienko and E. Dagotto, Phys. Rev. B 73, 094434 (2006).
[4] Y. Nishiwaki, T. Nakamura, A. Oosawa, K. Kakurai, N. Todoroki,
N. Igawa, Y. Ishii, and T. Kato, J. Phys. Soc. Jpn. 77, 104703 (2008).
[5] K. Morishita, T. Kato, K. Iio, T. Mitsui, M. Nasui, T. Tojo, and T.
Atake, Ferroelectrics 238, 105 (2000).
Authors
M. Tokunaga and Y. NishiwakiaaTokyo Women’s Medical University

References[1] D. Gatteschi et al., “Molecular Nanomagnets” (Oxford University
Press, 2006).
[2] L. Thomas et al., Nature 383, 145 (1996).
[3] C. Sangregorio et al., Phys. Rev. Letters 78, 4645 (1997).
[4] J. Schnack and M. Luban, Phys. Rev. B 63, 014418 (2000).
[5] D. Gatteschi et al., Nature (London) 354, 463 (1991).
[6] O. Cador et al., Angew. Chem. Int. Ed. 43, 5196 (2004).
Authors
Y. Furukawaa, K. Kumagaib, Y. Ajiroc, Y. Narumid, K. Kindo, P.
Santinie, F. Borsaf, R. E. P. WinpennygaIowa State Universityb
Hokkaido UniversitycKyoto UniversitydIMR, Tohoku UniversityeUniversita di Parmaf
Universita di Pavia
g
University of Manchester

Fig. 2. Magnetic phase diagram of RbCoBr3 for H || c-axis. The
schematic drawing in the inset demonstrate the possible spin structure
within the ab-plane in each phase.

Fig. 1. (a) A Magnetization curve (blue) and differential susceptibility(red) of RbCoBr3 at 4.2 K in a pulsed magnetic field of 55 T appliedalong the c-axis. We assigned two anomalies in the differential susceptibility as marked by the triangles. Crystallographic structure of the
RbCoBr3 is schematically drawn in the inset. (b) Field dependence ofthe differential susceptibilities in the field-increasing process at various
temperatures. The plot for each temperature was offset for clarity.

ISSP Activity Report 200843

International Conferences and Workshops

International Spring School on “Sub-10 nm Wires”

May 28-30, 2008
Y. Hasegawa, F. Komori, Y. Kuk, Q. Xue, J. Yoshinobu, and S. Hasegawa

Electronic states and transport in molecules and nanowires have recently attracted much attention The aim of the presentinternational spring school was to introduce fundamental knowledge on physics and chemistry of low-dimensional electronicsystems for young researchers in this interdisciplinary field of nanoscience. It was co-organized by A3 Foresight Program“Sub-10 nm Wires” and ISSP.
The school consisted of the following three lectures on electronic states and transport properties in low dimensional
systems, and a poster session.
(A) Quantum Transport
Professor Tsuneya Ando (Tokyo Institute of Technology)
Over view and details of theoretical approaches on the quantum transport were given with a focus on carbon nanotubes
and a few layer graphenes.
(B) Quantum Physics of Thin Metal Films
Professor Tai-Chang Chiang (University of Illinois)
Quantization of the electron energy levels in metallic thin films was discussed from the principle of photoelectron
spectroscopy to the detailed analyses of interface scattering.
(C) Fundamentals of Nanoelectronics
Professor Supriyo Datta (Purdue University)
Fundamentals and his original methods on quantum transport were given including advanced discussion on spintransport and energy dissipation.
More than 200 students (51 from abroad) attended the lectures, and 50 posters were presented. This school was financially
supported by JSPS, NSFC, KOSEF and ISSP.

Topological Aspects of Solid State Physics

June 2-22, 2008
M. Kohmoto and M. Oshikawa

As the third in the series of International Workshops organized by ISSP theory group, “Topological Aspects of Solid State
Physics” (TASSP) was held for the first three weeks of June 2008 at ISSP. In the following week (June 23 – June 27), a Symposium with the same title was held at Yukawa Institute for Theoretical Physics (YITP), Kyoto University. The Workshop part andthe Symposium part were sponsored by ISSP and YITP, recpectively. Both parts were also sponsored by Institute for Complex
Adaptive Matter (ICAM-I2CAM) with U.S. NSF Grant DMR-064546. The number of registered participants in the entire
period was 110 (72 in the Workshop at ISSP), including 26 invited participants (17 in the Workshop at ISSP) from overseas. In
this report, we mostly focus on the activities in the Workshop at ISSP, which was co-chaired by Mahito Kohmoto and Masaki
Oshikawa of ISSP with support from many people inside and outside ISSP.
Application of topological notion to condensed matter physics started several decades ago. One of the most notable
examples is quantum Hall effect, where the quantization of a physical quantity (Hall conductance) may be understood in termsof topological invariant (Chern number). Recently, more variety of systems is found to exhibit exotic quantum behaviors, andideas based on topology appear to be essential in understanding them. These include spin quantum Hall effect, graphenes,
topological phases of quantum spin systems. While each of these subjects is certainly worth individual attention, the purpose ofthis Workshop was to cultivate unified understanding of those diverse phenomena, based on topological concepts.
Reflecting the concept of the Workshop, there was a wide range of subjects of talks. While the Workshop is largely oriented
for theorists, three talks were given by experimentalists at ISSP to discuss their recent results from the topological perspective. There were 22 talks during the three weeks of Workshop at ISSP, and on average there were more than 20 people in theaudience for each talk.
The main aim of the Workshop was to encourage informal discussions and collaborations. In order to serve the purpose, at
most only two talks were scheduled each day to leave ample time for discussion. This format was well received by the participants, and in fact we could always hear lively discussion during the free time. As an outcome, several publications based oncollaborations initiated at the Workshop have been already reported.
The program and other details of the Workshop, including videos of the talks, can be found at the Workshop web page URL
http://www.issp.u-tokyo.ac.jp/public/TASSP/index.html

Supercomputing in Solid State Physics 2009

February 16-19, 2009
N. Kawashima, H. Noguchi, O. Sugino, T. Suzuki, Y. Tomita, S. Tsuneyuki, and Y. Yoshimoto

Every year, we host a domestic workshop in which most of the heavy users of the ISSP supercomputers get together andexchange new ideas. At the end of the school year 2008, the present supercomputer system is finishing its 4th year of thecurrent 5 year lease contract. We considered that this would be a good opportunity to have an international event by extending
our annual workshop, in order to review most important recent results in computational physics and stimulate further developments in both methodology and applications. With this background, we invited 40 speakers including 12 from overseas. In
addition to the oral presentations by the invited speakers, there are 46 poster presentations. Everyday we had audience of 80-90
who participated in lively discussions. Reflecting the diverse spectrum of the users of the ISSP supercomputer, a number of
topics were picked up from various fields of physics, including hydrogen storage systems, ultra-cold atoms in laser traps, flowof blood cells, and even initial formation of the universe. In spite of this diversity, however, we discovered a lot of knowledge
and techniques that are, or can be, shared by many apparently different fields, which was one of the main objectives of theevent.
URL: http://www.issp.u-tokyo.ac.jp/public/scissp/

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ISSP Workshops
Charge Fluctuation and Nonlinear Conduction of Molecular Conductors

May 21, 2008
I. Terasaki, Y. Nogami, M. Ogata, H. Seo, T. Kato, and H. Mori

Nonlinear conduction of charge-ordered molecular conductors is a hot topic in these days. Owing to the electric field
response of charge fluctuation, the threshold voltage is low, so that the intrinsic non-equilibrium state can be studied. As aresult, the dc-ac converter (synchronization) as an organic thyristor and the appearance of the metastable state, namely key
words of non-equilibrium system, have been observed. In this workshop, the recent progress of experimental and theoreticalresults, development of materials, dynamical crystal structure analyses under electric field, optical measurements, time-resolved
nonlinear conduction, nonlinear conduction under magnetic field, theoretical studies of nonlinear conduction, etc., has been
discussed. More than 66 researchers have joined and had hot discussions. The participants commented that this workshop isvery educational about recent progress of nonlinear conduction. We hope that this fruitful workshop triggers the new development of our researches.

International Spring School on “Sub-10 nm Wires”

May 28-30, 2008
F. Komori, Y. Hasegawa, J. Yoshinobu, Y. Kuk, Q. Xue, and S. Hasegawa

This ISSP workshop was held as a part of the international workshop of the same title. The school consisted of the threelectures on electronic states and transport properties in low dimensional systems, and a poster session by the participants. The
details are given in the section of “International Conferences and Workshops”.

The 2nd Workshop on the Science and Technology Based on the Advanced Coherent
Light Sources: “Progress of Photon Science at Extreme Wavelengths”

March 2-3, 2009
T. Suemoto

The laser based coherent light sources in the extreme ultraviolet and soft X ray regions have been developed at ISSP, Riken,
JAEA and some other research institutes in Japan. The available photon energy is now extended to several hundreds electron
volts at the high energy side and the shortest pulse width reaches in the range of one hundred attoseconds. High photon flux
and high stability are achieved and the new innovative technologies such as fiber lasers accelerate the field. Using these newly
developed laser light sources, novel spectroscopic methods such as attosecond molecular spectroscopy, high resolution photoelectron spectroscopy, inner shell non-linear spectroscopy, ultrafast imaging are proposed and some of them are demonstrated.
In order to take initiative in this new field of photon science and widen the application, ISSP and the Graduate School of
Frontier Sciences propose an establishment of "Advanced Coherent Light Laboratory" at Kashiwa campus. This workshop has
been organized to present this Kashiwa plan to the large audience outside the university and to encourage the development of
this new field by the close collaboration among the laser engineers, solid state physicists and synchrotron users. Twenty presentations are given in the sessions (1) Short wavelength lasers and their prospects (2) Research using short wavelength lasers, (3)From synchrotron radiation to lasers (4) From visible to shorter wavelengths (5) Exploration of new physics. During the free
discussion time, four talks initiated discussions on the necessity of a middle scale facility for photon science. The total numberof attendants on the first and the second day amounted to 130.

Design and Sciences of the KEK-Todai Chopper Spectrometer Project

March 18, 2009
T. J. Sato

The neutron science laboratory of the institute for solid state physics (ISSP-NSL) has been promoting the user program
as well as its own research programs using the JRR-3 research reactor. On the other hand, there is an on-going effort torealize an intense spallation neutron source, J-PARC/MLF, just beside the reactor, which will be fully operational in very near
future. On this occasion of achieving two different-type sources, ISSP-NSL has initiated construction of a chopper spectrometer at the spallation source, jointly with the neutron science laboratory of the high-energy accelerator research organization(KEK-KENS).
The chopper spectrometer covers wide E-Q range with realizing high-energy-resolution and high-counting-rate modes byselecting suitable chopper devices for the different necessities. It is partly based on the HRC spectrometer of KEK-KENS,
which has been under construction, and on VINS which has been planned by ISSP-NSL. In this workshop, we discuss the
spectrometer specifications of the joint project, as well as possible scientific opportunities that can be enabled by its enlarged
capability.

Recent Developments in the Physics of Heavy Fermions

July 23-25, 2008
T. Sakakibara, Y. Onuki, T. Takabatake, Y. Matsuda, H. Harima, T. Hotta, and H. Sato

Heavy-fermion systems have been extensively studied since the discovery in late 1970’s. It is now well established that
the Kondo effect of spin origin and the magnetic quantum criticality are important ingredients of the heavy-fermion states.
This “classical” view of heavy fermions has recently been challenged by the discovery of f-electron compounds whose mass
enhancement is quite immune to strong magnetic fields. This suggests a new mechanism for the formation of heavy fermionspossibly arising from multipole degrees of freedom and/or a rattling motion of atoms. This workshop was organized to bring
together researchers working in this field to discuss various new aspects of the heavy-fermion physics as well as new developments in experimental techniques. Topics discussed in the workshop included dHvA and PES experiments on heavy fermions,heavy-fermion superconductors, multipole orderings and fluctuations, rattling properties, heavy-fermion theories and newmaterials. We had 245 participants in total, and 45 oral and 25 poster presentations were given in the workshop.

Supercomputing in Solid State Physics 2009

February 16-19, 2009
N. Kawashima, H. Noguchi, O. Sugino, T. Suzuki, Y. Tomita, S. Tsuneyuki, and Y. Yoshimoto

See the section of “International Conferences and Workshops”.

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