Strategy for Direct Detection of Chiral Phonons with Phase-Structured Free Electrons

TL;DR

This paper proposes a novel method using phase-structured free electrons to directly detect chiral phonons with valley pseudo angular momentum, overcoming limitations of traditional electron energy loss techniques.

Contribution

Introduction of pinwheel free electron states with well-defined pseudo angular momentum to selectively probe chiral phonons.

Findings

Pinwheel free electrons generate in-plane field vortices with specific polarization textures.

The method enables direct detection of chiral phonons with valley pseudo angular momentum.

It overcomes previous measurement limitations in momentum-resolved electron energy loss spectroscopy.

Abstract

Chiral phonons possessing valley pseudo angular momentum (PAM) underlie a diversity of quantum phenomena of fundamental and applied importance, but are challenging to probe directly. We show that deficiencies of typical momentum-resolved electron energy loss measurements that make it impossible to distinguish the PAM of chiral phonons can be overcome by introducing pinwheel free electron states with well-defined PAM. Transitions between such states generate 2D periodic arrays of in-plane field vortices with polarization textures tailored to selectively couple to desired chiral mode symmetries.