Spin Nernst and thermal Hall effects of topological triplons in quantum dimer magnets on the maple-leaf and star lattices

We theoretically study the spin Nernst and thermal Hall effects of triplon excitations in quantum dimer magnets on the maple-leaf [1, 2] and star lattices [3]. These systems can be described by a spin-1/2 model with Heisenberg and Dzyaloshinskii-Moriya (DM) interactions in a magnetic field. Our findings reveal that without the in-plane DM vector: (i) at zero magnetic field, the band topology is characterized by a nontrivial Z_2 number, leading to the spin Nernst effect; and (ii) with a finite magnetic field, each band carries a nonzero Chern number, resulting in the thermal Hall effect of triplons. We derive analytical expressions for the spin Nernst and thermal Hall conductivities in the low-temperature regime. Moreover, when the DM vector has an in-plane component, we identify multiple phases with distinct band topologies as the magnetic field varies. These results can serve as a guide for future experiments.

[1] Y. Haraguchi et al., Phys. Rev. B 98, 064412 (2018).

[2] Y. Haraguchi et al., Phys. Rev. B 104, 174439 (2021).

[3] H. Ishikawa et al., Phys. Rev. B 109, L180401 (2024).