Spin-Liquid--to--Spin-Liquid Transition in Kitaev Magnets Driven by Fractionalization

TL;DR

This paper uncovers a first-order liquid-liquid transition between two distinct spin liquids in Kitaev magnets, driven by fractionalized excitations and topological changes, with implications for other perturbed Kitaev systems.

Contribution

It demonstrates a novel liquid-liquid transition between spin liquids in Kitaev magnets induced by Ising coupling and bond asymmetry, involving topological change and fractionalization.

Findings

First-order transition between two spin liquids identified.

Transition involves topological change driven by fractionalized excitations.

Transition line persists at finite temperatures, ending at a critical point.

Abstract

While phase transitions between magnetic analogs of three states of matter --- a long-range ordered state, paramagnet, and spin liquid --- have been extensively studied, the possibility of "liquid-liquid" transitions, namely, between different spin liquids, remains elusive. By introducing the additional Ising coupling into the honeycomb Kitaev model with bond asymmetry, we discover that the Kitaev spin liquid turns into a spin-nematic quantum paramagnet before a magnetic order is established by the Ising coupling. The quantum phase transition between the two liquid states accompanies a topological change driven by fractionalized excitations, the $Z_2$ gauge fluxes, and is of first order. At finite temperatures, this yields a persisting first-order transition line that terminates at a critical point located deep inside the regime where quantum spins are fractionalized. It is suggested that similar transitions may occur in other perturbed Kitaev magnets with bond asymmetry.