Manipulation of spin-polarized electronic states of two-dimensional (2D) materials under ambient conditions is necessary for developing new quantum devices with small physical dimensions. Here, we explore spin-dependent electronic structures of ultra-thin films of recently introduced 2D synthetic materials MSi2Z4 (M = Mo or W and Z = N or As) using first-principles modeling. Stacking of MSi2Z4 monolayers is found to generate dynamically stable bilayer and bulk materials with thickness-dependent properties. When spin-orbit coupling (SOC) is included in the computations, MSi2N4 monolayers display indirect bandgaps and large spin-split states at the K and K′ symmetry points at the corners of the Brillouin zone with nearly 100\% spin polarization. The spins are locked in opposite directions along an out-of-the-plane direction at K and K′, leading to spin-valley coupling effects. As expected, spin polarization is absent in the pristine bilayers due to the presence of inversion symmetry, but it can be induced via an external out-of-plane electric field much like the case of Mo(W)S2 bilayers. A transition from an indirect to a direct bandgap can be driven by replacing N by As in MSi2(N, As)4 monolayers. Our study indicates that the MSi2Z4 materials can provide a viable alternative to the MoS2 class of 2D materials for valleytronics and optoelectronics applications.
@article{arxiv.2105.02739,
title = {Tunable spin polarization and electronic structure of bottom-up synthesized MoSi$_2$N$_4$ materials},
author = {Rajibul Islam and Barun Ghosh and Carmine Autieri and Sugata Chowdhury and Arun Bansil and Amit Agarwal and Bahadur Singh},
journal= {arXiv preprint arXiv:2105.02739},
year = {2021}
}
Comments
6 pages, 5 figures, Accepted version in PRB:Letters