磁気液晶の発見(Discovery of magnetic liquid crystal)

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2023-12-14 韓国基礎科学研究院(IBS)

◆韓国のIBS Center for Artificial Low Dimensional Electronic Systemsの研究チームが、液晶の磁気アナログである「スピン・ネマティック位相」において、半世紀前に予測されたが直接観測されていなかった「スピンクアドルポールモーメント」を初めて直接観測した。これは、イリジウム酸化物Sr2IrO4を用い、先進のX線技術によって実現された。
◆スピン・ネマティック位相の発見は、量子コンピューティングや情報技術に影響を与え、また高温超伝導への可能性も示唆されている。キム・ボムジュン教授は、韓国のX線実験の進展によりこの研究が可能になったと述べ、P.W.アンダーソンの提案に基づく高温超伝導の重要性も強調されている。

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正方格子イリジウムの量子スピンネマチック位相 Quantum spin nematic phase in a square-lattice iridate

Hoon Kim,Jin-Kwang Kim,Junyoung Kwon,Jimin Kim,Hyun-Woo J. Kim,Seunghyeok Ha,Kwangrae Kim,Wonjun Lee,Jonghwan Kim,Gil Young Cho,Hyeokjun Heo,Joonho Jang,C. J. Sahle,A. Longo,J. Strempfer,G. Fabbris,Y. Choi,D. Haskel,Jungho Kim,J. -W. Kim & B. J. Kim
Nature  Published:13 December 2023
DOI:https://doi.org/10.1038/s41586-023-06829-4

磁気液晶の発見(Discovery of magnetic liquid crystal)

Abstract

Spin nematic is a magnetic analogue of classical liquid crystals, a fourth state of matter exhibiting characteristics of both liquid and solid1,2. Particularly intriguing is a valence-bond spin nematic3,4,5, in which spins are quantum entangled to form a multipolar order without breaking time-reversal symmetry, but its unambiguous experimental realization remains elusive. Here we establish a spin nematic phase in the square-lattice iridate Sr2IrO4, which approximately realizes a pseudospin one-half Heisenberg antiferromagnet in the strong spin–orbit coupling limit6,7,8,9. Upon cooling, the transition into the spin nematic phase at TC ≈ 263 K is marked by a divergence in the static spin quadrupole susceptibility extracted from our Raman spectra and concomitant emergence of a collective mode associated with the spontaneous breaking of rotational symmetries. The quadrupolar order persists in the antiferromagnetic phase below TN ≈ 230 K and becomes directly observable through its interference with the antiferromagnetic order in resonant X-ray diffraction, which allows us to uniquely determine its spatial structure. Further, we find using resonant inelastic X-ray scattering a complete breakdown of coherent magnon excitations at short-wavelength scales, suggesting a many-body quantum entanglement in the antiferromagnetic state10,11. Taken together, our results reveal a quantum order underlying the Néel antiferromagnet that is widely believed to be intimately connected to the mechanism of high-temperature superconductivity12,13.

1700応用理学一般
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