Detection of chiral spin fluctuations driven by frustration in Mott insulators

TL;DR

This study uses exact diagonalization to analyze resonant Raman scattering in frustrated Mott insulators, revealing signatures of chiral spin fluctuations and proximity to chiral spin liquid states.

Contribution

It demonstrates how resonant Raman scattering, especially in the $A_{2g}$ channel, can detect chiral fluctuations in frustrated Mott insulators, a novel application of this technique.

Findings

Increased spin frustration softens the $A_{2g}$ Raman response.

Chiral spin fluctuations are enhanced near the Mott gap.

Proximity to chiral spin liquids can be tuned by external perturbations.

Abstract

Topologically ordered states, such as chiral spin liquids, have been proposed as candidates that host fractionalized excitations. However, detecting chiral character or proximity to these non-trivial states remains a challenge. Resonant Raman scattering can be a powerful tool for detecting chiral fluctuations, as the $A_{2g}$ channel probes excitations with broken time-reversal symmetry and local chiral order. Here, we use exact diagonalization to characterize the resonant $A_{2g}$ channel, alongside two-magnon scattering in $B_{1g}$ and $E_g$ channels, for the Hubbard model on lattices with increasing levels of geometric spin frustration, where tuning the incident energy near the Mott gap reveals strong chiral spin excitation intensity. Increased spin frustration in the Mott insulator results in an overall softening of the Raman $A_{2g}$ response, indicating a tendency toward low energy chiral-chiral fluctuations in Mott insulators with magnetic frustration and proximity to chiral spin liquid states that can potentially be tuned by external perturbations.