Momentum relaxation effects in 2D-Xene field effect device structures

TL;DR

This paper investigates how momentum relaxation and dephasing affect the topological phase transitions and transport properties in 2D-Xene field effect devices, providing insights for realistic device modeling.

Contribution

It introduces a detailed analysis of topological phase transitions in 2D-Xene under electric fields considering momentum relaxation, using the Keldysh Green's function method with new metrics for stability.

Findings

Quantum spin Hall edge states show moderate decay with relaxation.

Effective transmission is key to analyzing topological stability.

Dephasing induces band-tails, reducing ON-OFF ratios.

Abstract

We analyze the electric field driven topological field effect transition on 2D-xene materials with the addition of momentum relaxation effects, in order to account for dephasing processes. The topological field effect transition between the quantum spin Hall phase and the quantum valley Hall phase is analyzed in detail using the Keldysh non-equilibrium Green's function technique with the inclusion of momentum and phase relaxation, within the self-consistent Born approximation. Details of the transition with applied electric field are elucidated for the ON-OFF characteristics with emphasis on the transport properties along with the tomography of the current carrying edge states. We note that for moderate momentum relaxation, the current carrying quantum spin Hall edge states are still pristine and show moderate decay with propagation. To facilitate our analysis, we introduce two metrics in our calculations, the coherent transmission and the effective transmission. In elucidating the physics clearly, we show that the effective transmission, which is derived rigorously from the quantum mechanical current operator is indeed the right quantity to analyze topological stability against dephasing. Exploring further, we show that the insulating quantum valley Hall phase, as a result of dephasing carries band-tails which potentially activates parasitic OFF currents, thereby degrading the ON-OFF ratios. Our analysis sets the stage for realistic modeling of topological field effect devices for various applications, with the inclusion of scattering effects and analyzing their role in the optimization of the device performance.