Origin of Immediate Damping of Coherent Oscillations in Photoinduced Charge Density Wave Transition

TL;DR

This study uses real-time simulations to explain the immediate damping of coherent oscillations in a photoinduced charge density wave transition on In/Si(111), revealing the role of electron promotion and bond switching.

Contribution

It demonstrates, through rt-TDDFT simulations, the microscopic mechanism behind the rapid damping of CDW oscillations in a one-dimensional surface system.

Findings

Photoexcitation promotes electrons from Si substrate to surface bands.

Structural transition involves switching among covalent In bonds.

Damping of oscillations results from a rotation of interatomic forces.

Abstract

In stark contrast to the conventional charge density wave (CDW) materials, the one-dimensional CDW on the In/Si(111) surface exhibits immediate damping of the CDW oscillation during the photoinduced phase transition. Here, by successfully reproducing the experimentally observed photoinduced CDW transition on the In/Si(111) surface by performing real-time time-dependent density functional theory (rt-TDDFT) simulations, we demonstrate that photoexcitation promotes valence electrons from Si substrate to empty surface bands composed primarily of the covalent p-p bonding states of the long In-In bonds, generating interatomic forces to shorten the long bonds and in turn drives coherently the structural transition. We illustrate that after the structural transition, the component of these surface bands occurs a switch among different covalent In bonds, causing a rotation of the interatomic forces by about {\pi}/6 and thus quickly damping the oscillations in feature CDW modes. These findings provide a deeper understanding of photoinduced phase transitions.