Dielectric response in twisted MoS2 bilayer facilitated by spin-orbit coupling effect

Abstract

Twisted van der Waals bilayers offer ideal two-dimensional (2D) platforms for exploring the intricate interplay between the spin and charge degrees of freedom of electrons. By investigating twisted MoS2 bilayer, featuring two distinct stackings but with identical commensurate supercell sizes, we reveal an unusual dielectric response behavior inherent to this system. Our first-principles calculations demonstrate that the application of an out-of-plane electric field gives different responses in electronic polarization. Upon further analysis, it becomes apparent that this dielectric response comes from the planar charge redistribution associated with spin-orbit coupling (SOC) effect. The underlying mechanism lies in the fact that the external electric field tends to modify the internal pseudo-spin texture \sigma, subsequently generating an out-of-plane (pseudo-) spin current j_s \propto \sigma \times B_R as response to an in-plane pseudomagnetic field B_R through Rashba SOC. It is found that the generated j_s is opposite for the two distinct stackings, resulting in opposite in-plane electric susceptibility. As a consequence, through magnetoelectric coupling within such nonmagnetic system, there give rise to opposite tendency to redistribute charge, ultimately leading to an amplified or suppressed dielectric response.