Prediction of protected band edge states and dielectric tunable quasiparticle and excitonic properties of monolayer MoSi$_2$N$_4$

TL;DR

This paper demonstrates that monolayer MoSi$_2$N$_4$ has robust band edge states resistant to environmental chemical effects, while its quasiparticle and excitonic properties can be tuned via dielectric screening, making it promising for electronic and optoelectronic applications.

Contribution

It reveals that MoSi$_2$N$_4$ possesses environmentally robust band edge states and tunable quasiparticle properties through dielectric screening, supported by detailed many-body calculations.

Findings

Band edge states are protected from chemical coupling effects.

Quasiparticle and excitonic properties can be modulated by dielectric environment.

MoSi$_2$N$_4$ is thermodynamically and mechanically stable.

Abstract

The electronic structure of two-dimensional (2D) materials are inherently prone to environmental perturbations, which may pose significant challenges to their applications in electronic or optoelectronic devices. A 2D material couples with its environment through two mechanisms: local chemical coupling and nonlocal dielectric screening effects. The local chemical coupling is often difficult to predict or control experimentally. Nonlocal dielectric screening, on the other hand, can be tuned by choosing the substrates or layer thickness in a controllable manner. Therefore, a compelling 2D electronic material should offer band edge states that are robust against local chemical coupling effects. Here it is demonstrated that the recently synthesized MoSi$_2$N$_4$ is an ideal 2D semiconductor with robust band edge states protected from capricious environmental chemical coupling effects. Detailed many-body perturbation theory calculations are carried out to illustrate how the band edge states of MoSi$_2$N$_4$ are shielded from the direct chemical coupling effects, but its quasiparticle and excitonic properties can be modulated through the nonlocal dielectric screening effects. This unique property, together with the moderate band gap and the thermodynamic and mechanical stability of this material, paves the way for a range of applications of MoSi$_2$N$_4$ in areas including energy, 2D electronics, and optoelectronics.