Weak-coupling to strong-coupling quantum criticality crossover in a Kitaev quantum spin liquid alpha-RuCl3

Abstract

We report a quantum criticality crossover representing two different universal scaling behaviors in a Kitaev quantum magnetic material alpha-RuCl3. alpha-RuCl3 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 unique universality class involving deconfined fractionalized excitations of the local Z(2) fluxes and itinerant Majorana fermions. Theoretical analyses on the inelastic neutron scattering, ac-magnetic susceptibility, 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 quantum criticality evolves in fermion-boson coupled topological systems with different types of deconfined fermions.