Influence of interface induced valley-Zeeman and spin-orbit couplings on transport in heterostructures of graphene on WSe2

Abstract

We investigate the electronic dispersion and transport properties of graphene/${\mathrm{WSe}}_{2}$ heterostructures in the presence of a proximity induced spin-orbit coupling (SOC) using a low-energy Hamiltonian, with different types of symmetry breaking terms, obtained from a four-band, first and second nearest-neighbour tight-binding (TB) one. The competition between different perturbation terms leads to inverted SOC bands. Further, we study the effect of symmetry breaking terms on ac and dc transport by evaluating the corresponding conductivities within linear response theory. The scattering-independent part of the valley-Hall conductivity, as a function of the Fermi energy ${E}_{F}$, is mostly negative in the ranges $\ensuremath{-}{\ensuremath{\lambda}}_{R}\ensuremath{\leqslant}{E}_{F}$ and ${E}_{F}\ensuremath{\geqslant}{\ensuremath{\lambda}}_{R}$ when the strength ${\ensuremath{\lambda}}_{R}$ of the Rashba SOC increases except for a very narrow region around ${E}_{F}=0$ in which it peaks sharply upward. The scattering-dependent diffusive conductivity increases linearly with electron density, is directly proportional to ${\ensuremath{\lambda}}_{R}$ in the low- and high-density regimes, but weakens for ${\ensuremath{\lambda}}_{R}=0$. We investigate the optical response in the presence of a SOC-tunable band gap for variable ${E}_{F}$. An interesting feature of this SOC tuning is that it can be used to switch on and off the Drude-type intraband response. Furthermore, the ac conductivity exhibits interband responses due to the Rashba SOC. We also show that the valley-Hall conductivity changes sign when ${E}_{F}$ is comparable to ${\ensuremath{\lambda}}_{R}$ and vanishes at higher values of ${E}_{F}$. It also exhibits a strong dependence on temperature and a considerable structure as a function of the frequency.