Weak-coupling to strong-coupling quantum criticality crossover in a Kitaev quantum spin liquid $\alpha$-RuCl$_3$

TL;DR

This study reveals a crossover between weak and strong coupling quantum critical behaviors in the Kitaev quantum spin liquid candidate $ ext{α}$-RuCl$_3$, highlighting the evolution of quantum criticality in a topological magnetic system.

Contribution

It uncovers a novel quantum criticality crossover in $ ext{α}$-RuCl$_3$, demonstrating a transition from weak-coupling to strong-coupling universality classes involving fractionalized excitations.

Findings

Identification of two distinct universal scaling behaviors

Observation of a crossover from Wilson-Fisher-Yukawa to heavy-fermion-type criticality

Insights into quantum criticality evolution in fermion-boson coupled topological systems

Abstract

We report an unprecedented quantum criticality crossover representing two different universal scaling behaviors in a Kitaev quantum magnetic material $\alpha$-RuCl$_3$. $\alpha$-RuCl$_3$ presents both a symmetry breaking antiferromagnetic order and a long-range entangled topological order of a quantum spin liquid, and thus could be a candidate system for a new universality class involving deconfined fractionalized excitations of the local Z$_2$ fluxes and itinerant Majorana fermions. Theoretical analyses on the inelastic neutron scattering and specific heat results demonstrate that Wilson-Fisher-Yukawa-type 'conventional' weak-coupling quantum criticality in high energy scales crosses over to heavy-fermion-type 'local' strong-coupling one in low energy scales. Our findings provide deep insight on how the quantum criticality evolves in fermion-boson coupled topological systems with different types of deconfined fermions.