Eur. Phys. J. B (2013) 86: 391
https://doi.org/10.1140/epjb/e2013-40482-7

Regular Article

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

Institut für Physik, Universität Augsburg, 86135 Augsburg, Germany

^a e-mail: ziegler@physik.uni-augsburg.de

Received: 13 May 2013
Received in final form: 29 June 2013
Published online: 23 September 2013

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.