Dielectric response of laser-excited silicon at finite electron temperature

TL;DR

This study uses adiabatic TDDFT to analyze the dielectric response of laser-excited silicon at finite electron temperatures, revealing negative low-frequency behavior and short electron collision times.

Contribution

It provides a first-principles calculation of the dielectric response of excited silicon at finite temperature, comparing with pump-probe simulations and Drude model fittings.

Findings

Negative dielectric response at low frequencies due to electron-hole pairs

Effective electron masses range from 0.22 to 0.36

Electron lifetimes range from 1 to 14 femtoseconds

Abstract

We calculate the dielectric response of excited crystalline silicon in electron thermal equilibrium by adiabatic time-dependent density functional theory (TDDFT) to model the response to irradiation by high-intensity laser pulses. The real part of the dielectric function is characterized by the strong negative behavior at low frequencies due to excited electron-hole pairs. The response agrees rather well with the numerical pump-probe calculations which simulate electronic excitations in nonequilibrium phase immediately after the laser pulse irradiation. The thermal response is also compared with the Drude model which includes electron effective mass and collision time as fitting parameters. We find that the extracted effective masses are in the range of 0.22-0.36 and lifetimes are in the range of 1-14 fs depending on the temperature. The short Drude lifetimes show that strong damping is possible in the adiabatic TDDFT, despite the absence of explicit electron-electron collisions.