Chiral tricritical point: a new universality class in Dirac systems

TL;DR

This paper introduces a new universality class called the chiral tricritical point (CTP) in Dirac systems, arising from the coupling of tricritical Ising models with massless Dirac fermions, and analyzes its critical behavior.

Contribution

It identifies and characterizes a novel universality class at the tricritical point in Dirac systems, extending understanding of fermion-induced critical phenomena.

Findings

Discovery of the chiral tricritical point (CTP) at the phase boundary.

Critical behaviors of CTP are distinct from known universality classes.

Extension of analysis to Heisenberg spins and discussion of experimental relevance.

Abstract

Tricriticality, as a sister of criticality, is a fundamental and absorbing issue in condensed matter physics. It has been verified that the bosonic Wilson-Fisher universality class can be changed by gapless fermionic modes at criticality. However, the counterpart phenomena at tricriticality have rarely been explored. In this paper, we study a model in which a tricritical Ising model is coupled to massless Dirac fermions. We find that the massless Dirac fermions result in the emergence of a new tricritical point, which we refer to as the chiral tricritical point (CTP), at the phase boundary between the Dirac semimetal and the charge-density-wave insulator. From functional renormalization group analysis of the effective action, we obtain the critical behaviors of the CTP, which are qualitatively distinct from both the tricritical Ising universality and the chiral Ising universality. We further extend the calculations of the chiral tricritical behaviors of Ising spins to the case of Heisenberg spins. The experimental relevance of the CTP in two-dimensional Dirac semimetals is also discussed.