PRESS RELEASETokyo, 13 February 2020
Studying Electrons, Bridging Two Realms of Physics: Connecting Solids and Soft
MatterScientists explain how exotic phenomena involving electrons in certain solid systems are similar
to particles in certain liquid systems or soft matter
Condensed matter physics, which analyzes the behavior of electrons in organized solid matter,has been treated as a completely separate field of study from soft matter physics, which deals
with liquids, gels, etc. But in a new study, researchers from Japan have now revealed that undercertain special conditions, the electrons in solid matter exhibit similar properties to theconstituent particles of soft matter.
Electrons are interesting particles that can modify their behavior according to their condition of existence.
For instance, in a phenomenon called the Mott-transition, electrons begin to interact differently with theirneighbors and surroundings in a material. Normally, the electrons in a material have low levels ofinteraction with each other and therefore, move freely enough for the material to conduct electricity (andthe material shows metallic properties). But under certain conditions, these same electrons begin to havehigh levels of interaction with each other and their movement becomes restricted. This causes thematerial to become an insulator. The alteration of the properties of the material is called the Motttransition.
At the Mott-transition, certain phenomena such as high-temperature superconductivity and giant
magnetoresistance are seen, which have massive industrial applications. Thus, studying these phenomena
is essential. But to truly discover these phenomena, it is important to understand electron behavior indisordered materials (materials in which the arrangement of the constituent particles is interrupted atpoints over the long range).
A group of scientists from Tokyo University of Science, The University of Tokyo, and Tohoku University inJapan, led by Prof Tetsuaki Itou, recently set out to investigate exactly this. They used a quasi-twodimensional organic Mott-insulator called ĸ-(ET)2Cu[N(CN)2]Cl (hereafter ĸCl), whose disorder andelectron interaction level they independently controlled by irradiating the material with x-rays andapplying pressure, respectively. When they irradiated ĸCl with x-rays for 500 hours, they found thatelectron movement slowed down by a factor ranging from one million to one hundred million. This meantthat its electrons begin to behave peculiarly, as though they’re the constituent particles of soft matter(e.g., polymers, gels, cream, etc.). When the scientists applied pressure on the irradiated ĸCl, the electron
behavior returned to normal.

From these observations, the scientists deduced that for electrons in solids to behave like the particles ofsoft matter, two factors are essential: the material must be in the vicinity of the Mott-transition point andthere must be disorder. The simultaneous existence of these two factors is a manifestation of aphenomenon similar to the Griffiths phase, which has already been established for magnetic materials.
What the researchers found here is evidence for its electronic analog: the electronic Griffiths phase. “Ourresults provide experimental evidence that the Griffiths scenario is also applicable to Mott-transitionsystems” remarks Prof Itou.
This exciting new study is published in Physical Review Letters under “Editors' Suggestion”, which issuggested by the journal when the study is interesting and important. The study represents a bridge
between condensed matter physics and soft matter physics, which have hitherto developed completelyindependently. “We expect that, with the publication of our study, further discussions linking thesedisciplines will be carried out,” says Prof Itou. The insights gained from this study may allow scientists toexplain the mechanisms underlying these exotic phenomena, which could have very powerful applications,
not the least of which involves opening doors to whole new possibilities in a much wider realm of physics.

Fig. 1. Temperature-pressure-randomness phase diagram of a Mott transition system, as proposed inthis study. In the electonic Griffiths phase, the electrons in the solid material behave like the particles ofsoft matter.

ReferenceAuthors:

Title of original paper:
Journal:DOI:
Affiliations:

Riku Yamamoto1, Tetsuya Furukawa1, Kazuya Miyagawa2, Takahiko
Sasaki3, Kazushi Kanoda2 and Tetsuaki Itou1*
Electronic Griffiths Phase in Disordered Mott-Transition Systems
Physical Review Letters
https://www.doi.org/10.1103/PhysRevLett.124.046404
1
Department of Applied Physics, Tokyo University of Science, JapanDepartment of Applied Physics, The University of Tokyo, Japan
Institute for Materials Research, Tohoku University, Japan

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Further Information
Professor Testuaki Itou
Department of Applied Physics
Tokyo University of Science
Email: tetsuaki.itou@rs.tus.ac.jp
Professor Takahiko Sasaki
Institute for Materials ResearchTohoku University
Email: takahiko@imr.tohoku.ac.jp
Professor Kazushi Kanoda
Department of Applied Physics
The University of Tokyo
Email: kanoda@ap.t.u-tokyo.ac.jp
Media contact
Tsutomu Shimizu
Public Relations Divisions
Tokyo University of Science
Email: mediaoffice@admin.tus.ac.jp
Website: https://www.tus.ac.jp/en/mediarelations/
Institute for Materials ResearchTohoku University
Email: pro-adm@imr.tohoku.ac.jp
Office of Public Relations
School of Engineering
The University of Tokyo
Email: kouhou@pr.t.u-tokyo.ac.jp
Funding information
This work was supported in part by the Japan Society for the Promotion of Science Grants-in-Aidfor Scientific Research (Grant Nos. 25220709, 17K05532, 18H05225, and 19H01833).