Thermal Hall effect in a van der Waals ferromagnet CrI3

CrI3 is a prototypical van der Waals ferromagnet with a magnetic honeycomb lattice. Previous inelastic neutron scattering studies have suggested topological nature of its magnetic excitations with a magnon gap at the Dirac points, which are anticipated to give rise to magnon thermal Hall effect. Here we report thermal transport properties of CrI3 and show that the long-sought thermal Hall signal anticipated for topological magnons is fairly small. In contrast, we find that CrI3 exhibits an appreciable anomalous thermal Hall signal at lower temperature which may arise from magnon-phonon hybridization or magnon-phonon scattering. These findings are anticipated to stimulate further neutron scattering studies on CrI3 single crystal, which can shed light not only on the intrinsic nature of magnetic excitations but also on the magnon-phonon interaction. Data for the figures presented in this paper are available at this link.CrI3是一种典型的范德华铁磁体（van der Waals ferromagnet），具有蜂巢状磁晶格（magnetic honeycomb lattice）。此前的非弹性中子散射（inelastic neutron scattering）研究表明，其磁激发具有拓扑特性，在狄拉克点（Dirac points）处存在磁振子能隙（magnon gap），该特性有望引发磁振子热霍尔效应（magnon thermal Hall effect）。本文报道了CrI3的热输运（thermal transport）特性，结果显示，长期追寻的拓扑磁振子对应热霍尔信号相当微弱。与之相反，我们发现在低温下CrI3呈现出显著的反常热霍尔信号，该信号可能源自磁振子-声子杂化（magnon-phonon hybridization）或磁振子-声子散射（magnon-phonon scattering）。上述研究成果有望推动针对CrI3单晶（single crystal）的进一步中子散射研究，这不仅有助于阐明磁激发的本征特性，也能为磁振子-声子相互作用（magnon-phonon interaction）提供新的认知。 本文配图所用数据可通过该链接获取。