量子スピン液体の検証方法を確立～磁場の方向で温まりやすさが変化することに着目～

2025-03-17 東京大学,東北大学

量子スピン液体のイメージ図
量子スピン液体状態では、磁場の方向（オレンジ矢印）を変えたときの比熱が特異的に変化する。

＜関連情報＞

• https://www.k.u-tokyo.ac.jp/information/category/press/11474.html
• https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.134.106701

Na2Co2TeO6の電界角度分解比熱：Kitaev量子スピン液体に対する証拠 Field-Angle-Resolved Specific Heat in Na2⁢Co2⁢Te⁢O6: Evidence against Kitaev Quantum Spin Liquid

Shengjie Fang, Kumpei Imamura, Yuta Mizukami, Ryuichi Namba, Kota Ishihara, Kenichiro Hashimoto, and Takasada Shibauchi
Physical Review Letters  Published: 13 March, 2025
DOI:https://doi.org/10.1103/PhysRevLett.134.106701

Abstract

Kitaev quantum spin liquids (KSLs) in layered honeycomb magnets are known to host Majorana quasiparticles, whose excitations depend strongly on the direction of the applied magnetic field. In the high-field phase of −RuCl₃, specific heat measurements have revealed characteristic field-angle dependence of low-energy excitations consistent with the Kitaev model, providing bulk evidence for the KSL state. Here we present low-temperature measurements of specific heat () for another KSL candidate Na₂⁢Co₂⁢Te⁢O₆ (NCTO) under field rotation within the honeycomb plane. Above the critical field of antiferromagnetic order, the field-angle dependence of / exhibits minima along the bond directions, contrasting with the maxima observed in the KSL state of −RuCl₃. Our analysis indicates nodeless, fully gapped excitations, which are inconsistent with the angle-dependent Majorana excitations with gapless nodes predicted by the Kitaev model. These findings suggest that low-energy excitations in NCTO are governed by gapped magnon excitations rather than Majorana quasiparticles, providing thermodynamic evidence against a KSL state.