Controllable spin direction in nonmagnetic BX/MX2 (M = Mo or W; X = S, Se and Te) van der Waals heterostructures by switching between the Rashba splitting and valley polarization

Abstract

Manipulating the physical properties using the spin degree of freedom constitutes a major part of modern condensed matter physics and is a key aspect of spintronic devices. Using density functional theory calculations, we predict that the spin direction can be controlled in nonmagnetic BX/MX₂ (M = Mo or W; X = S, Se and Te) van der Waals heterostructures. The stability of the heterostructures is confirmed by calculating their binding energies and phonon dispersion plots. The electronic structures of the heterostructures demonstrate that all of them maintain the semiconducting nature, but have different band alignment, which is related to orbital components at the band-edge and influenced by electron transfer at the interface. By considering the spin–orbit coupling, the Rashba-type spin splitting with the in-plane spin and valley polarization with the out-of-plane spin can be formed and coexist at the valence-bands of BSe/MoSe₂ and BSe/WSe₂. Moreover, the dominant carrier spin direction around the valence-band edge can be effectively tuned by exerting a biaxial strain and external electrical field. These calculations show that manipulation of the spin within semiconductor devices to exploit the full potential of materials with a gap for charge control without the use of auxiliary ferromagnetic materials and magnetic fields can be achieved in the newly discovered two-dimensional van der Waals system.