Quantum Multicriticality in Disordered Weyl Semimetal

TL;DR

This paper uncovers a novel disorder-driven multicritical point in Weyl semimetals, revealing complex phase transitions among Weyl semimetal, Chern insulator, and diffusive metal phases through theoretical and numerical analysis.

Contribution

It introduces a new critical theory describing a disorder-induced multicritical point in Weyl semimetals, detailing phase boundaries and transition properties.

Findings

Identification of a disorder-driven multicritical point in Weyl semimetals.

Numerical confirmation of phase transition classes and critical exponents.

Analysis of localization-delocalization transitions among three quantum phases.

Abstract

In electronic band structure of solid state material, two band touching points with linear dispersion appear in pair in the momentum space. When they annihilate with each other, the system undergoes a quantum phase transition from three-dimensional Weyl semimetal (WSM) phase to a band insulator phase such as Chern band insulator (CI) phase. The phase transition is described by a new critical theory with a `magnetic dipole' like object in the momentum space. In this paper, we reveal that the critical theory hosts a novel disorder-driven quantum multicritical point, which is encompassed by three quantum phases, renormalized WSM phase, CI phase, and diffusive metal (DM) phase. Based on the renormalization group argument, we first clarify scaling properties around the band touching points at the quantum multicritical point as well as all phase boundaries among these three phases. Based on numerical calculations of localization length, density of states and critical conductance distribution, we next prove that a localization-delocalization transition between the CI phase with a finite zero-energy density of states (zDOS) and DM phase belongs to an ordinary 3D unitary class. Meanwhile, a localization-delocalization transition between the Chern insulator phase with zero zDOS and a renormalized Weyl semimetal (WSM) phase turns out to be a direct phase transition whose critical exponent $\nu=0.80\pm 0.01$. We interpret these numerical results by a renormalization group analysis on the critical theory.