Dynamical symmetry breaking in a 2D electron gas with a spectral node

TL;DR

This paper investigates the effects of disorder on a 2D electron gas with a spectral node, revealing how dynamical symmetry breaking influences conductivity and provides a detailed description of minimal and V-shaped conductivities.

Contribution

It introduces a nonlinear sigma model approach to analyze dynamical symmetry breaking and its impact on conductivity in disordered 2D electron systems with spectral nodes.

Findings

DC conductivity increases linearly with quasiparticle density.

Provides a comprehensive description of minimal conductivity at the Dirac node.

Describes V-shaped conductivity inside the bands.

Abstract

We study a disordered 2D electron gas with a spectral node in a vicinity of the node. After identifying the fundamental dynamical symmetries of this system, the spontaneous breaking of the latter by a Grassmann field is studied within a nonlinear sigma model approach. This allows us to reduce the average two-particle Green's function to a diffusion propagator with a random diffusion coefficient. The latter has non-degenerate saddle points and is treated by the conventional self-consistent Born approximation. This leads to a renormalized chemical potential and a renormalized diffusion coefficient, where the DC conductivity increases linearly with the density of quasiparticles. Applied to the special case of Dirac fermions, our approach provides a comprehensive description of the minimal conductivity at the Dirac node as well as for the V-shape conductivity inside the bands.