Impurity quadrupole moments as local probes of flux sectors in the Kitaev spin liquid

TL;DR

This paper demonstrates that impurity quadrupole moments can directly probe flux configurations in the Kitaev spin liquid, revealing flux sector transitions and flux stability through impurity measurements.

Contribution

It introduces a method using impurity quadrupole moments as local probes for flux sectors in the Kitaev spin liquid, linking impurity properties to flux configurations.

Findings

Impurity quadrupole moments exhibit discontinuous jumps at flux sector transitions.

Quadrupole correlations decay exponentially with flux-dependent rates.

The stability of pi fluxes bound to impurities is analyzed in relation to model parameters.

Abstract

Emergent fluxes play a central role in the low-energy properties of quantum spin liquids (QSLs), where they encode the underlying gauge structure and fractionalization of spins. Here, we show that the quadrupole moment of magnetic impurities provides a direct probe of these flux configurations in QSLs. Employing the SO(6) Majorana representation for spin-3/2 impurity operators in the isotropic Kitaev spin liquid together with a self-consistent mean-field approximation for impurity-related terms, we show that the ground-state flux sector can be identified by discontinuous jumps of the impurity quadrupole moment at the flux sector transition points. We also demonstrate that the quadrupole correlations between impurities under a magnetic field exhibit exponential decay, with decay rates that depend sensitively on the flux sector. Furthermore, we discuss the stability of pi fluxes bound to impurities with respect to model parameters and internal flux configurations, and relate our findings to Lieb's conjecture on flux configurations. These results establish the quadrupole moments of magnetic impurities as a sensitive tool to study fractionalized excitations and flux physics in Kitaev magnets.