Emergence of a Field-Driven U(1) Spin Liquid in the Kitaev Honeycomb Model

TL;DR

This paper maps out the phase diagram of the Kitaev honeycomb model under tilted magnetic fields, revealing a new gapless U(1) spin liquid phase characterized by gapless fermions coupled to a gauge field.

Contribution

It identifies and characterizes a novel field-driven U(1) spin liquid phase in the Kitaev model, expanding understanding of quantum spin liquids in magnetic fields.

Findings

Discovery of a gapless U(1) spin liquid phase.

Evidence of gapless fermions coupled to a U(1) gauge field.

Phase diagram mapping under tilted magnetic fields.

Abstract

In the field of quantum magnetism, the exactly solvable Kitaev honeycomb model serves as a paradigm for the fractionalization of spin degrees of freedom and the formation of $\mathbb{Z}_2$ quantum spin liquids. An intense experimental search has led to the discovery of a number of spin-orbit entangled Mott insulators that realize its characteristic bond-directional interactions and, in the presence of magnetic fields, exhibit no indications of long-range order. Here, we map out the complete phase diagram of the Kitaev model in tilted magnetic fields and report the emergence of a distinct gapless quantum spin liquid at intermediate field strengths. Analyzing a number of static, dynamical, and finite temperature quantities using numerical exact diagonalization techniques, we find strong evidence that this phase exhibits gapless fermions coupled to a massless $U(1)$ gauge field. We discuss its stability in the presence of perturbations that naturally arise in spin-orbit entangled candidate materials.