Spinon Phonon Interaction and Ultrasonic Attenuation in Quantum Spin Liquids

TL;DR

This paper explores how ultrasonic attenuation can be used to detect spinon properties and pairing transitions in quantum spin liquids, providing a new experimental probe for these elusive states.

Contribution

It demonstrates that spinons couple to phonons similarly to electrons, enabling ultrasonic measurements to reveal spinon mass, lifetime, and pairing onset in quantum spin liquids.

Findings

Ultrasonic attenuation can measure spinon mass and lifetime.

Transverse ultrasonic attenuation drops sharply at the pairing transition.

The Meissner effect causes a rapid fall in attenuation below T_c.

Abstract

Several experimental candidates for quantum spin liquids have been discovered in the past few years which appear to support gapless fermionic $S = {1\over 2}$ excitations called spinons. The spinons may form a Fermi sea coupled to a $U(1)$ gauge field, and may undergo a pairing instability. We show that despite being charge neutral, the spinons couple to phonons in exactly the same way that electrons do in the long wavelength limit. Therefore we can use sound attenuation to measure the spinon mass and lifetime. Furthermore, transverse ultrasonic attenuation is a direct probe of the onset of pairing because the Meissner effect of the gauge field causes a "rapid fall" of the attenuation at $T_c$ in addition to the reduction due to the opening of the energy gap. This phenomenon, well known in clean superconductors, may reveal the existence of the U(1) gauge field.