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Direct observation of the mystery of “Hidden Order” in condensed-matter physics

Crystal structure change in a uranium-based material clarified

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Graduate School of Frontier Sciences
2014/06/25

The research team of Professor Takasada Shibauchi and Assitant Professor Yuta Mizukami in the Department of Advanced Materials Science at the University of Tokyo Graduate School of Frontier Sciences and Professor Yuji Matsuda in the Kyoto University Graduate School of Science have observed directly that the crystal structure in the enigmatic “hidden order” phase of the uranium compound URu2Si2 is slightly deformed to an orthorhombic (diamond-like) shape with twofold rotational symmetry by ultra-high resolution synchrotron crystal-structure analysis at the Spring-8 synchrotron radiation facility.

Schematic diagram of the electronic state of the “hidden order”.

© 2014 Takasada Shibauchi.
Schematic diagram of the electronic state of the “hidden order”. Gray spheres are uranium atoms, around which the electronic state exhibits ellipsoidal anisotropy, being different on the left and right diagonals, breaking fourfold symmetry in the basal plane (blue).

The nature of this so-called “hidden order” electronic state in URu2Si2 is a 30-year-old mystery in condensed-matter physics. Previously, the research group had obtained indirect evidence that the crystal structure possessed twofold symmetry, but previous research had reported a tetragonal square shape with fourfold symmetry. The present direct observation of the crystal structure change clarifies decisively the mystery as to the space symmetry exhibited by the electronic structure of the hidden-order state. The space symmetry found reveals a nontrivial electronic state, which will pave the way for understanding of new electronic states of matter.

This research was conducted in collaboration with the groups of Kunihisa Sugimoto, Researcher in Japan Synchrotron Radiation Research Institute, and Yoshinori Haga, Chief Scientist in Japan Atomic Energy Agency.

This research was published online in the British science journal Nature Communications on 19 June 2014.

Press release (Japanese)

Paper

S. Tonegawa, S. Kasahara, T. Fukuda, K. Sugimoto, N. Yasuda, Y. Tsuruhara, D. Watanabe, Y. Mizukami, Y. Haga, T.D. Matsuda, E. Yamamoto, Y. Onuki, H. Ikeda, Y. Matsuda, T. Shibauchi,
“Direct observation of lattice symmetry breaking at the hidden-order transition in URu2Si2”,
Nature Communications vol.5, Article number: 4188 (2014), doi: 10.1038/ncomms5188.
Article link

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Graduate School of Frontier Sciences

Department of Advanced Materials Science, Graduate School of Frontier Sciences

Shibauchi Laboratory, Department of Advanced Materials Science, Graduate School of Frontier Sciences

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