Giant spin Nernst effect in a two-dimensional antiferromagnet due to magnetoelastic coupling induced gaps and interband transitions between magnonlike bands
D. Quang To, C. Y. Ameyaw, Abhin Suresh, Subhash Bhatt, Mark Ku, M. Benjamin Jungfleisch, John Q. Xiao, J. M. O. Zide, Branislav K. Nikolić, Matthew F. Doty
Abstract
We analyze theoretically the origin of the spin Nernst and thermal Hall effects in ${\mathrm{FePS}}_{3}$ as a realization of a two-dimensional antiferromagnet (2D AFM). We find that a strong magnetoelastic coupling, hybridizing magnetic excitations (magnons) and elastic excitations (phonons), combined with time-reversal symmetry breaking, results in Berry curvature hotspots in the region of anticrossing between the two distinct hybridized bands. Furthermore, a large spin Berry curvature emerges due to interband transitions between two magnonlike bands, where a small energy gap is induced by magnetoelastic coupling between such bands that are energetically distant from anticrossings of hybridized bands. These nonzero Berry curvatures generate topological transverse transport (i.e., the thermal Hall effect) of hybrid excitations, dubbed magnon-polarons, as well as of the spin (i.e., the spin Nernst effect) carried by them, in response to an applied longitudinal temperature gradient. We investigate the dependence of the spin Nernst and thermal Hall conductivities on the applied magnetic field and temperature, unveiling a very large spin Nernst conductivity even at zero magnetic field. Our results suggest the ${\mathrm{FePS}}_{3}$ AFM, which is already available in 2D form experimentally, as a promising platform to explore the topological transport of magnon-polaron quasiparticles at terahertz frequencies.