Direct observation of two-phonon bound states in ZnTe

TL;DR

This paper reports the first time-domain observation of a coherent two-phonon bound state in ZnTe, generated via second-order Raman scattering, revealing new insights into phonon interactions and coherence in this material.

Contribution

It demonstrates impulsive generation and characterization of two-phonon bound states in ZnTe using time-resolved spectroscopy, a novel experimental achievement.

Findings

Observation of a two-phonon bound state with full {a1} symmetry

Coexistence of bound and unbound two-phonon states demonstrated

Energy of bound state exceeds 2TA(X) overtone

Abstract

A coherent two-phonon bound state has been impulsively generated in ZnTe(110) via second-order Raman scattering in the time domain for the first time. The two-phonon bound state, composed of two anticorrelated in wave vector acoustic phonons, exhibits full {\Gamma}1 symmetry and has energy higher than the corresponding 2TA(X) overtone. By suppressing two-phonon fluctuations with a double-pulse excitation, the coexistence of coherently excited bound and unbound two-phonon states has been demonstrated.