Impurity effects and bandgap-closing in massive Dirac systems

TL;DR

This paper studies how disorder and impurity scattering affect the spectral properties of massive Dirac systems, revealing a critical impurity strength where the bandgap closes and a finite density of states appears at zero energy.

Contribution

It demonstrates that impurity-induced dynamical renormalization causes bandgap closing in massive Dirac systems, independent of the effective mass vanishing, emphasizing the role of incoherent processes.

Findings

Bandgap closes at a critical impurity strength $U_c$.

Finite density of states emerges at zero energy after gap closing.

Incoherent processes are essential for understanding the physics of gap closing.

Abstract

We investigate the effects in the spectral properties of a massive Dirac system of the dynamical renormalization induce by disorder/impurity scattering within the self-consistent Born approximation. We show how that these effects leads to a remarkable closing of the bandgap edge. Above a critical value $U_c$ of the impurity scattering the gap eventually closes, giving rise a finite density of states at zero energy. We show that the bandgap closing stems from the quasi-particle dynamical renormalization and it is not associated with the vanishing of the effective massive term. Incoherent processes are fundamental to describe such physics.