Spectroscopic fingerprints of gapped quantum spin liquids, both conventional and fractonic

TL;DR

This paper demonstrates how multidimensional coherent spectroscopy can uniquely identify and distinguish between various gapped quantum spin liquids, including conventional and fractonic types, through their distinct spectroscopic signatures.

Contribution

It introduces a method to unambiguously diagnose gapped quantum spin liquids using existing spectroscopy techniques, highlighting differences between conventional and fractonic phases.

Findings

Two-dimensional coherent spectroscopy reveals signatures of conventional spin liquids.

Type I fracton phases show clear spectroscopic features even in linear response.

Type II fracton systems require high-order non-linear response analysis.

Abstract

We explain how gapped quantum spin liquids, both conventional and 'fractonic', may be unambiguously diagnosed experimentally using the technique of multidimensional coherent spectroscopy. 'Conventional' gapped quantum spin liquids (e.g. $Z_2$ spin liquid) do not have clear signatures in linear response, but do have clear fingerprints in non-linear response, accessible through the already existing experimental technique of two dimensional coherent spectroscopy. Type I fracton phases (e.g. X-cube) are (surprisingly) even easier to distinguish, with strongly suggestive features even in linear response, and unambiguous signatures in non-linear response. Type II fracton systems, like Haah's code, are most subtle, and may require consideration of high order non-linear response for unambiguous diagnosis.