Anomalous critical state of electrons near a metal-insulator boundary
Discovery of quantum criticality of Mott transition
Graduate School of Engineering / Faculty of Engineering
Electrons in materials are subject to repulsive interactions due to their negative charges. Sufficiently strong repulsive interactions make electrons keep away from each other and localized, so that the particle-like electrons exhibit what is called a Mott insulating state. In contrast, the interactions, when weakened, cause the electrons to be disentangled from the localized states and move freely; the wave-like electrons form a metal. This phenomenon is called the Mott transition, and brings about many anomalous phenomena such as high-temperature superconductivity in cuprates. Recently, the quantum critical phenomena of electrons on the verge of the Mott transition, in which microscopic metallic and Mott-insulating regions fluctuate temporally and spatially in an interchangeable manner, have been studied theoretically and were awaiting experimental demonstration.
A research group centered on Dr. Tetsuya Furukawa, Assistant Professor Kazuya Miyagawa and Professor Kazushi Kanoda at the Graduate School of Engineering of the University of Tokyo has experimentally discovered the quantum criticality of the Mott transition. The electric resistivity for three types of molecular crystals, which have different properties at temperatures near absolute zero, was measured under high pressure. The group demonstrated, for the first time, that the resistivity at temperatures of dozens of Kelvin obeys the scaling relation characterizing quantum critical phenomena of the Mott transition.
The result brings a new perspective that the materials near a metal-insulator boundary fall into various material-dependent metallic or insulating phases at low temperatures but exhibit material-independent universal critical states at high temperatures.
Quantum criticality of Mott transition in organic materials", Nature Physics: 2015/2/10 (Japan time), doi: 10.1038/nphys323.
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