Optical conductivity of visons in Z2 spin liquids close to a VBS transition on the kagome lattice

TL;DR

This paper investigates how vison excitations in Z2 spin liquids near a VBS transition on the kagome lattice influence optical conductivity, revealing a specific power law behavior linked to quantum criticality.

Contribution

It demonstrates that visons can couple to electromagnetic fields via magneto-elastic effects, affecting optical conductivity near VBS transitions, a novel insight into spin liquid excitations.

Findings

Finite ac-conductivity shows a power law frequency dependence for 36-site VBS transitions.

Visons do not contribute to optical conductivity at 12-site VBS transitions.

Coupling mechanism enables vison detection through optical measurements.

Abstract

We consider Z2 spin liquids on the kagome lattice on the verge of a valence bond solid (VBS) transition, where vortex excitations carrying Z2 magnetic flux - so-called visons - condense. We show that these vison excitations can couple directly to the external electromagnetic field, even though they carry neither spin nor charge. This is possible via a magneto-elastic coupling mechanism recently identified by Potter et al and Hao. For the case of transitions to a 36-site unit cell VBS state the corresponding finite ac-conductivity has a specific power law frequency dependence, which is related to the crossover exponent of the quantum critical point. The visons' contribution to the optical conductivity at transitions to VBS states with a 12-site unit cell vanishes, however.