Phase transitions in 3-dimensional Dirac semi-metals using Schwinger-Dyson equations

TL;DR

This paper investigates the quantum phase transition in 3D Dirac semi-metals, highlighting how different theoretical approximations affect the predicted critical coupling and the potential role of anisotropy in gap formation.

Contribution

It demonstrates that the critical coupling's dependence on anisotropy varies significantly with the approximation scheme used for photon polarization, emphasizing the need for full photon dynamics.

Findings

Critical coupling varies with anisotropy depending on approximation methods.

Including full photon dynamics is essential for accurate predictions.

Anisotropy may facilitate dynamical gap generation in realistic materials.

Abstract

We study the semi-metal/insulator quantum phase transition in three-dimensional Dirac semi-metals by solving a set of Schwinger-Dyson equations. We study the effect of an anisotropic fermion velocity on the critical coupling of the transition. We consider the influence of several different approximations that are commonly used in the literature and show that results for the critical coupling change considerably when some of these approximations are relaxed. Most importantly, the nature of the dependence of the critical coupling on the anisotropy depends strongly on the approximations that are used for the photon polarization tensor. On the one hand, this means that calculations that include full photon dynamics are necessary to answer even the basic question of whether the critical coupling increases or decreases with anisotropy. On the other hand, our results mean that it is possible that anisotropy could provide a mechanism to promote dynamical gap generation in realistic three-dimensional Dirac semi-metallic materials.