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

Source: [Dynamical symmetry breaking in a 2D electron gas with a spectral node](<https://www.sota2.com/research/paper/68fa2cb21e209131ce8524bf>)

Collection index: [llms.txt](<https://www.sota2.com/research/llms.txt>)

Data updated: 2025-10-24T15:30:04.780Z

Authors: K. Ziegler

Published: 2012-07-16T14:57:58.000Z

## 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.

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## Original sources and implementation

[Original paper](<https://arxiv.org/abs/1207.3701>)

[PDF](<https://arxiv.org/pdf/1207.3701.pdf>)