Anomalous Cherenkov spin-orbit sound

TL;DR

This paper predicts a novel anomalous Cherenkov sound phenomenon in systems with spin-orbit interactions, featuring both forward and backward sound propagation, and suggests its use for measuring spin-orbit coupling strength.

Contribution

It introduces the concept of anomalous Cherenkov sound caused by spin-orbit interactions and describes its singular transition at the Cherenkov cone angle.

Findings

Presence of backward Cherenkov sound in addition to normal forward sound.

Singular transition at the Cherenkov cone angle.

Potential for experimental measurement of spin-orbit coupling.

Abstract

The Cherenkov effect is a well known phenomenon in the electrodynamics of fast charged particles passing through transparent media. If the particle is faster than the light in a given medium, the medium emits a forward light cone. This beautiful phenomenon has an acoustic counterpart where the role of photons is played by phonons and the role of the speed of light is played by the sound velocity. In this case the medium emits a forward sound cone. Here, we show that in a system with spin-orbit interactions in addition to this {\it normal} Cherenkov sound there appears an {\it anomalous} Cherenkov sound with forward and {\it backward} sound propagation. Furthermore, we demonstrate that the transition from the normal to anomalous Cherenkov sound happens in a {\it singular} way at the Cherenkov cone angle. The detection of this acoustic singularities therefore represents an alternative experimental tool for the measurement of the spin-orbit coupling strength.