Prediction of Janus XYSTe (X=Li, Na; Y=Al, Ga, In) monolayers with tunable Rashba effect for spintronic devices

Janus two-dimensional materials with sizable and tunable Rashba spin-splitting are of utmost importance in the next-generation spintronic devices. In this paper, First-principles calculations are performed to predict a new group of Janus monolayers XYSTe (X = Li, Na; Y=Al, Ga, In) with inherent structural asymmetry. Phonon spectral calculations, ab initio molecular dynamic simulations, and cohesive energies demonstrate that all the proposed structures are stable. XYSTe monolayers are found to be semiconductors with large bandgaps ranging from 1.75 to 3.48 eV, from HSE06 functional calculations. Broken mirror symmetry in the proposed Janus structures induces an out-of-plane intrinsic electric field which is confirmed by electrostatic potential and Bader charge population analysis. The electric field results in a distinct Rashba spin-splitting at the high symmetry P- point of the lowest conduction band of all XYSTe monolayers. The Rashba coefficients of the proposed monolayers are in the range of 0.94-1.40 eVA(center dot) rendering them as auspicious candidates for spintronic devices. It is also found that the bandgap and Rashba effect can be tuned by employing biaxial strain and the Rashba coefficient can be up to 1.56 eVA(center dot) in NaGaSTe monolayer. Finally, the tunability of Rashba splitting with an external electric field is demonstrated. Our results show that the Janus XYSTe monolayers are potential materials for two-dimensional spintronic devices.