カゴメ金属における“電流の一方通行” 新原理を発見～ミクロな電流ループを活用した新しい量子的な整流効果～

2025-08-26 名古屋大学

＜関連情報＞

• https://www.nagoya-u.ac.jp/researchinfo/result/2025/08/post-866.html
• https://www.nagoya-u.ac.jp/researchinfo/result/upload_images/20250826_sci.pdf
• https://www.pnas.org/doi/10.1073/pnas.2503645122

カゴメ金属のキラルループ電流相における量子メトリック誘起の巨大かつ可逆的な非互換輸送現象 Quantum metric–induced giant and reversible nonreciprocal transport phenomena in chiral loop-current phases of kagome metals

Rina Tazai, Youichi Yamakawa, Takahiro Morimoto, and Hiroshi Kontani
Proceedings of the National Academy of Sciences  Published:August 25, 2025
DOI:https://doi.org/10.1073/pnas.2503645122

Significance

Rich symmetry-breaking phenomena driven by nontrivial quantum geometry are central topics in condensed matter physics. In particular, the chiral loop-current order observed in kagome metals and cuprate superconductors has attracted significant attention. Notably, the giant electrical magnetochiral anisotropy (eMChA) observed in kagome metals provides compelling evidence for the breaking of time-reversal and inversion symmetries. Here, we demonstrate that the eMChA is proportional to the loop-current-induced orbital magnetization, which is reversible by the magnetic field. Remarkably, the quantum metric exhibits significant momentum dependence in the loop-current phase, leading to the giant eMChA. This work not only sheds light on the fundamental symmetry-breaking mechanisms in kagome metals but also opens broad avenues for exploring quantum metric–induced phenomena resulting from exotic quantum phases.

Abstract

Emergence of quantum orders with nontrivial quantum geometric properties in metals represent central issues in condensed matter physics. In this context, recently discovered chiral loop-current order in kagome metals has garnered significant attention. Particularly noteworthy is the giant electrical magnetochiral anisotropy (eMChA) observed in CsV₃Sb₅, which provides compelling evidence for the simultaneous breaking of time-reversal and inversion symmetries. However, the origin of the eMChA and its fundamental connection to the loop-current remain highly elusive, as the loop-current itself preserves inversion symmetry. Here, we demonstrate that the loop-current phase breaks inversion symmetry in the presence of the experimentally observed stripe charge-density wave, leading to finite eMChA coefficient γ_eM. In this mechanism,γ_eM is proportional to the product of the loop-current-induced orbital magnetization,M⁰_orb , and the lifetime of conduction electrons, τ. Therefore,γ_eM is reversible by the magnetic fields, and it takes large value in kagome metals with ^TU _Fermi>>a(=lattice constant). Surprisingly, the quantum metric, which defines a fundamental geometric aspect of Bloch wavefunctions, acquires significant momentum dependence in the loop-current phase, resulting in a dramatic enhancement of eMChA by ∼100 times. This research not only clarifies the fundamental symmetry-breaking states in kagome metals but also opens a path for exploring quantum metric–induced phenomena arising from exotic quantum phase transitions in various metals.