A new scale anomaly in Dirac matter

TL;DR

This paper identifies a novel conformal anomaly in Dirac semimetals caused by the running of the Fermi velocity, impacting their thermodynamic and hydrodynamic properties, especially in graphene.

Contribution

It introduces a new scale anomaly in Dirac materials due to Fermi velocity renormalization, extending the understanding of conformal anomalies beyond charge renormalization.

Findings

Fermi velocity running induces a conformal anomaly.

The anomaly affects sound wave propagation in hydrodynamics.

It modifies thermodynamic equations of state and introduces bulk viscosity.

Abstract

The dynamics of Dirac semimetals is modeled at low energies by the massless Dirac Hamiltonian with the Fermi velocity replacing the velocity of light. The classical action is scale invariant. In 3D materials, Coulomb interactions induce a conformal anomaly associated to the charge renormalization already known in quantum field theory. In this work, we describe a new conformal anomaly induced by the running of the Fermi velocity that applies to Dirac semimetals in two and three dimensions. The case of graphene is particularly interesting. We analyze the anomaly and explore its thermodynamic and hydrodynamic consequences. The anomaly modifies the propagation speed of hydrodynamic sound waves, alters the thermodynamic equation of state, and induces a non-vanishing bulk viscosity proportional to the beta function of the Fermi velocity.