All-optically induced ultrafast photocurrents: Beyond the instantaneous coherent response

TL;DR

This paper reveals how non-instantaneous coherent polarization responses enable a new type of shift current in semiconductors, controllable with shaped ultrafast pulses, advancing understanding of light-matter interactions.

Contribution

It introduces a novel shift current mechanism dependent on phase mismatch and polarization shaping, expanding the understanding of nonlinear optical effects in semiconductors.

Findings

New shift current observed with polarization-shaped pulses

Current depends on phase mismatch between transition dipoles

Effect observable at room temperature in various semiconductors

Abstract

It is demonstrated that the non-instantaneous response of the optically induced coherent polarization tremendously influences the real-space shift of electronic charges in semiconductors. The possibility to coherently control this real-space shift with temporally non-overlapping excitation pulses allows for the observation of a new type of shift current, which only exists for certain polarization-shaped excitation pulses and vanishes in the continuous-wave limit. In contrast to previously studied shift currents, the new current requires a phase mismatch between two orthogonal transition dipole moments and leads, within a nonlinear second-order description, to a tensor which is antisymmetric with respect to the order of the two exciting electric field amplitudes. These observations, which can even be made at room temperature and are expected to occur in a variety of semiconductor crystal classes, contribute to a better understanding of light-matter interaction involving degenerate bands. Thus, they are expected to prove important for future studies of coherent and nonlinear optical effects in semiconductors.