The critical role of hot carrier cooling in optically excited structural transitions

TL;DR

This study highlights the crucial influence of hot carrier cooling on photoinduced phase transitions, demonstrating its role in atomic dynamics and phase change initiation in IrTe2 through advanced simulations.

Contribution

It introduces the inclusion of hot carrier cooling in rt-TDDFT simulations to better understand phase transition mechanisms.

Findings

Hot carrier cooling enhances atomic driving forces and kinetic energy.

Cooling induces nonradiative recombination, leading to ultrafast dimer recovery.

Hot carrier dynamics are essential for understanding photoinduced phase transitions.

Abstract

The hot carrier cooling occurs in most photoexcitation-induced phase transitions (PIPTs), but its role has often been neglected in many theoretical simulations as well as in proposed mechanisms. Here, by including the previously ignored hot carrier cooling in real-time time-dependent density functional theory (rt-TDDFT) simulations, we investigated the role of hot carrier cooling in PIPTs. Taking IrTe2 as an example, we reveal that the cooling of hot electrons from the higher energy levels of spatially extended states to the lower energy levels of the localized Ir-Ir dimer antibonding states strengthens remarkably the atomic driving forces and enhances atomic kinetic energy. These two factors combine to dissolute the Ir-Ir dimers on a timescale near the limit of atomic motions, thus initiating a deterministic kinetic phase transition. We further demonstrate that the subsequent cooling induces nonradiative recombination of photoexcited electrons and holes, leading to the ultrafast recovery of the Ir-Ir dimers observed experimentally. These findings provide a complete picture of the atomic dynamics in optically excited structural phase transitions.