Critical behavior of two-dimensional random hopping fermions with \pi-flux

TL;DR

This paper investigates the critical behavior of a two-dimensional random hopping fermion model with -flux, revealing its universality class, fixed points, and implications for localization and density of states.

Contribution

It identifies the universality class of the model and analyzes the fixed points, providing new insights into the delocalization and density of states at the band center.

Findings

Vanishing beta function indicates delocalized states at the band center.

Large N-systems are at a weak-coupling fixed point with divergent density of states.

Small N-systems may be at a strong-coupling fixed point.

Abstract

A two dimensional random hopping model with N-species and \pi-flux is studied. The field theory at the band center is shown to be in the universality class of GL(4m,R)/O(4m) nonlinear sigma model. Vanishing beta function suggests delocalised states at the band center. Contrary to the similar universality class with broken time reversal symmetry, the present class is expected to have at least two fixed point. Large N-systems are shown to be in the weak-coupling fixed point, which is characterized by divergent density of state, while small N systems may be in the strong-coupling fixed point.