Controlling ultrafast currents by the non-linear photogalvanic effect

TL;DR

This paper theoretically demonstrates how broken inversion symmetry in SiO2 enables ultrafast, controllable DC currents via a non-linear photogalvanic effect, with a current reversal at a critical laser intensity.

Contribution

It reveals a novel mechanism for ultrafast current control in dielectrics using strong laser pulses and identifies a threshold-induced current reversal phenomenon.

Findings

Ultrafast DC currents are generated by strong femtosecond laser pulses.

A sudden current reversal occurs above a critical laser intensity.

Ultrafast current control is robust against pulse shape and phase variations.

Abstract

We theoretically investigate the effect of broken inversion symmetry on the generation and control of ultrafast currents in a transparent dielectric (SiO2) by strong femto-second optical laser pulses. Ab-initio simulations based on time-dependent density functional theory predict ultrafast DC currents that can be viewed as a non-linear photogalvanic effect. Most surprisingly, the direction of the current undergoes a sudden reversal above a critical threshold value of laser intensity I_c ~ 3.8*10^13 W/cm2. We trace this switching to the transition from non-linear polarization currents to the tunneling excitation regime. We demonstrate control of the ultrafast currents by the time delay between two laser pulses. We find the ultrafast current control by the non-linear photogalvanic effect to be remarkably robust and insensitive to laser-pulse shape and carrier-envelope phase.