Unifying explanation for carrier relaxation anomaly in gapped systems

TL;DR

This paper presents a unified theory explaining the anomalous carrier relaxation times in gapped systems near transition temperatures, emphasizing the role of transverse acoustic phonons and validated by experimental data fitting.

Contribution

It introduces a comprehensive model for carrier relaxation in gapped systems, highlighting the impact of phonon heat capacity and providing a unified explanation for observed anomalies.

Findings

Transverse acoustic phonons significantly influence relaxation times.

The theory accurately fits experimental data from fullerene polymers.

Carrier relaxation time diverges near the transition temperature.

Abstract

We develop a theory to describe energy relaxation of photo-excited carriers in low-temperature ordered states with band gap opening and formulate carrier relaxation time $\tau$ near and below transition temperature $T_{\mathrm{c}}$ by quantifying contributions from different carrier-phonon scatterings to the relaxation rate. The theory explains anomalous experimental observations of $\tau$ in gapped systems. Transverse acoustic (TA) phonon modes play a crucial role in carrier relaxation; their heat capacity determines $\tau$-divergence near $T_{\mathrm{c}}$. The theory is validated by fitting $\tau$ of fullerene polymers onto a theoretical curve.