Observation of a dynamic magneto-chiral instability in photoexcited tellurium

TL;DR

This paper reports the experimental observation of a dynamic magneto-chiral instability in photoexcited tellurium, demonstrating THz wave amplification due to electromagnetic interactions with impurity states.

Contribution

It provides the first experimental evidence of a magneto-chiral instability in a chiral solid-state system and proposes a theoretical model explaining the amplification mechanism.

Findings

Detection of THz emission with coherent modes amplifying over time

Observation of a magneto-chiral instability in elemental tellurium

Theoretical model explaining amplification via impurity-induced polaritons

Abstract

In a system of charged chiral fermions driven out of equilibrium, an electric current parallel to the magnetic field can generate a dynamic instability by which electromagnetic waves become amplified. Whether a similar instability can occur in chiral solid-state systems remains an open question. Using time-domain terahertz (THz) emission spectroscopy, we detect signatures of what we dub a ``dynamic magneto-chiral instability" in elemental tellurium, a structurally chiral crystal. Upon transient photoexcitation in a moderate external magnetic field, tellurium emits THz radiation consisting of coherent modes that amplify over time. An explanation for this amplification is proposed using a theoretical model based on a dynamic instability of electromagnetic waves interacting with infrared-active oscillators of impurity acceptor states in tellurium to form an amplifying polariton. Our work not only uncovers the presence of a magneto-chiral instability but also highlights its promise for THz-wave amplification in chiral materials.