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Solving a 25-year puzzle in solid state physics

Emergent Rank-5 order in URu2Si2


Graduate School of Engineering / Faculty of Engineering

Schematic picture of the state with the hidden order clarified in the present study ©Hiroaki Ikeda

Phase transition is one of the central issues in condensed matter physics. Textbooks list a variety of examples, including magnetic phase transition, superconducting phase transition, and so on. In magnetic phase transition, spins in the solid align in various patterns. In the superconducting transition, electrons form so-called Cooper pairs. To describe these phase transitions mathematically, we introduce a parameter called the order parameter. Usually, it is not a difficult task to determine experimentally what kind of order appears at low temperatures. In 1985, it was discovered that URu2Si2 experiences a phase transition at 17.5K. Since then, extensive experimental and theoretical studies have been performed to clarify the mechanism of the phase transition. However, the order parameter of this phase transition has remained as a puzzle for the last 25 years. Professor Ryotaro Arita at the University of Tokyo’s Graduate School of Engineering, Department of Applied Physics, in collaboration with Hiroaki Ikeda, Takasada Shibauchi, and Yuji Matsuda at the Department of Physics, Kyoto University, Michi-To Suzuki at CCSE, Japan Atomic Energy Agency, and Tetsuya Takimoto at the Asia Pacific Center for Theoretical Physics, POSTECH Korea, carried out microscopic study for this hidden order. Starting with a non-empirical calculation for the electronic structure of this compound, they quantitatively evaluated the response functions for all possible order parameters. In general, f-electrons in heavy elements such as uranium have a large angular momentum, so that they can have various unique order parameters, termed multipole order. Indeed, in the present calculation, the researchers found that a rank-5 order is the strongest candidate. This result will provide new insights for a fundamental understanding of phase transition in materials.

Press release


H. Ikeda, M-T. Suzuki, R. Arita, T. Takimoto, T. Shibauchi, Y. Matsuda,
“Emergent rank-5 nematic order in URu2Si2″,
Nature Physics Advance online publication: [2012]/[6]/[4] (Japan time), doi: 10.10138/nphys2326.
Article link


Graduate School of Engineering

Department of Applied Physics

Arita Laboratory

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