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Discovery of “Nematic Liquid Crystal State of Electrons”: A Key to Elucidate the Working Mechanism of Fe-based High-Temperature Superconducting Materials (Press Release)

Release Date
21 Jun, 2012
  • BL02B1 (Single Crystal Structure Analysis)

Kyoto University
Japan Synchrotron Radiation Research Institute (JASRI)
Japan Atomic Energy Agency

Researchers at Kyoto University (president: Hiroshi Matsumoto), in collaboration with those at Japan Synchrotron Radiation Research Institute (JASRI; president: Tetsuhisa Shirakawa) and Japan Atomic Energy Agency (JAEA; president: Atsuyuki Suzuki), revealed an aspect of irregular properties of the electron state that serve as a backdrop on which high-temperature superconductivity manifests itself. The research group that accomplished the results included scientists at Graduate School of Science, Kyoto University (research fellow Shigeru Kasahara, associate professor Takasada Shibauchi, professor Yuji Matsuda), JASRI (research scientist Kunihisa Sugimoto), and JAEA (research fellow Tatsuo Fukuda).

The research results indicate that the electron population in a high-temperature superconductor makes spontaneous phase transition (*2) into a new state where the rotational symmetry of the crystal lattice is broken, at higher temperatures than those that trigger transition into a superconducting state. The state of broken electronic symmetry is called a “nematic electronic state” (*1) because of its similarity to that of nematic liquid crystals, which are often used in liquid crystal displays. Similar types of electronic structure have also been reported in studies on high-temperature cuprate superconductors, as well as those involving Fe atoms, as is reported here, suggesting the need to pay attention to the link between the nematic electronic state and the mechanism that develops superconductivity. Detailed information on the link may provide a clue to unravel one of the challenges still unresolved in modern condensed matter physics: the expression mechanism of high-temperature superconductivity.

The results were issued in the online publication (June 21) of the English scientific journal “Nature.”

Publication:
"Electronic nematicity above the structural and superconducting transition in BaFe2(As1-xPx)2"
S. Kasahara1,2, H. J. Shi1, K. Hashimoto1, S. Tonegawa1, Y. Mizukami1, T. Shibauchi1, K. Sugimoto3, T. Fukuda４, T. Terashima2, A. H. Nevidomskyy5 , Y. Matsuda1
1Department of Physics, Kyoto University, 2Research Center for Low Temperature and Materials Sciences, Kyoto University, 3JASRI/SPring-8, 4JAEA/SPring-8, 5Rice University
Nature 486, 382–385 (2012) Published online 20 June 2012

<<Figures>>

Fig. 1. The crystal structure of Fe-based superconductor BaFe2(As1-xPx)2
Fig. 1. The crystal structure of Fe-based superconductor BaFe2(As1-xPx)2

Fig. 2. Temperature-composition phase diagram of Fe-based superconductor BaFe2(As1-xPx)2 (Left)
Fig. 2. Temperature-composition phase diagram of Fe-based superconductor BaFe2(As1-xPx)2 (Left)

In the paramagnetic-tetragonal phase, the isotropic electronic state prevails (figure in upper right). In the electric nematic phase induced by breach of the rotational symmetry of the crystal lattice (anisotropy in electric system), the antiferromagnetic-orthorhombic phase spreads into higher temperature regions of the superconducting phase (figure in lower right).

Fig.3. Magnetic anisotropy measurement using a piezoresistive micro cantilever
Fig.3. Magnetic anisotropy measurement using a piezoresistive micro cantilever

High resolution measurement of Intra-magnetic surface anisotropy can be realized by placing a single crystal sample on the cantilever and by using vector magnets.

Fig.4. The large radius imaging plate camera equipment at SPring-8 BL02B1
Fig.4. The large radius imaging plate camera equipment at SPring-8 BL02B1

The capability of this equipment to measure a diffracted X-ray at high reflection angles enables high resolution analysis of minute crystal structure modifications.

<<Glossary>>
*1 Nematic state
A state of matter in which spatial arrangements of molecules do not have three-dimensional order but exhibit orientation order in a specific direction. For example, in the nematic liquid crystal - an aggregate of elongated molecules typically used in TV displays -, centers of molecules are randomly distributed, but the orientation of the molecules is aligned in one direction.

*2 Phase transition
The ice (solid) melts into water (liquid) as the temperature rises, and the water evaporates into vapor (gas) upon a further rising of temperature. Magnetic attraction suddenly disappears when the temperature reaches a certain level. This phenomena - the transformation of a system from one phase of matter to another - is called phase transition, and constitutes one of the major research areas of physics.


For more information, please contact:
　　Prof. Yuji Matsuda (Department of Physics, Kyoto University)
　　　　E-mail：
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