Thermal Hall effects due to topological spin fluctuations in YMnO3

• Published in: Nature communications Vol. 15; no. 1; p. 243
• Main Authors: Kim, Ha-Leem, Saito, Takuma, Yang, Heejun, Ishizuka, Hiroaki, Coak, Matthew John, Lee, Jun Han, Sim, Hasung, Oh, Yoon Seok, Nagaosa, Naoto, Park, Je-Geun
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 04.01.2024; Nature Publishing Group; Nature Portfolio
• Subjects: 639/301/119/2792; 639/766/119/997; Chirality; Electromagnetism; Elementary excitations; Fluctuations; Hall effect; Humanities and Social Sciences; Insulators; Magnetic fields; Magnetic structure; Magnons; multidisciplinary; Science; Science (multidisciplinary); Topology
• ISSN: 2041-1723; 2041-1723
• DOI: 10.1038/s41467-023-44448-9

The thermal Hall effect in magnetic insulators has been considered a powerful method for examining the topological nature of charge-neutral quasiparticles such as magnons. Yet, unlike the kagome system, the triangular lattice has received less attention for studying the thermal Hall effect because the scalar spin chirality cancels out between adjacent triangles. However, such cancellation cannot be perfect if the triangular lattice is distorted. Here, we report that the trimerized triangular lattice of multiferroic hexagonal manganite YMnO 3 produces a highly unusual thermal Hall effect under an applied magnetic field. Our theoretical calculations demonstrate that the thermal Hall conductivity is related to the splitting of the otherwise degenerate two chiralities of its 120˚ magnetic structure. Our result is one of the most unusual cases of topological physics due to this broken Z 2 symmetry of the chirality in the supposedly paramagnetic state of YMnO 3 , due to strong topological spin fluctuations with the additional intricacy of a Dzyaloshinskii-Moriya interaction. The thermal Hall effect has been reported in several materials, but it is not expected in triangular lattice systems due to chirality cancellation. Kim et al. report the thermal Hall effect attributed to topological spin fluctuations in the supposedly paramagnetic phase of YMnO 3 with a trimerized triangular lattice.