Spin-orbit and exchange proximity couplings in graphene/1T-TaS2 heterostructure triggered by a charge density wave

Abstract

Proximity-induced fine features and spin-textures of the electronic bands in graphene-based van der Waals heterostructures can be explored from the point of tailoring a twist angle. Here we study spin-orbit coupling and exchange coupling engineering of graphene states in the proximity of 1T-TaS2 not triggering the twist, but a charge density wave (CDW) in 1T-TaS2—a realistic low-temperature phase. Using density functional theory and effective model we found that the emergence of the CDW in 1T-TaS2 significantly enhances Rashba spin-orbit splitting in graphene and tilts the spin texture by a significant Rashba angle—in a very similar way as in the conventional twist-angle scenarios. Moreover, the partially filled Ta d-band in the CDW phase leads to the spontaneous emergence of the in-plane magnetic order that transgresses via proximity from 1T-TaS2 to graphene, hence, simultaneously superimposing along the spin-orbit also the exchange coupling proximity effect. To describe this intricate proximity landscape we have developed an effective model Hamiltonian and provided a minimal set of parameters that excellently reproduces all the spectral features predicted by the first-principles calculations. Conceptually, the CDW provides a highly interesting knob to control the fine features of electronic states and to tailor the superimposed proximity effects—a sort of twistronics without twist.