The optical phonoelectric effect

TL;DR

This paper introduces a strain-free, ultrafast optical phonoelectric effect driven by photo-excited phonons, surpassing traditional piezoelectric limitations in speed and amplitude, with potential for advanced optical control and device applications.

Contribution

The authors demonstrate a novel optical phonoelectric effect in BPO$_4$, enabling rapid, high-amplitude polarization without mechanical strain, overcoming piezoelectric constraints.

Findings

Optical phonoelectricity achieved in BPO$_4$ via phonon rectification.

Response speed exceeds traditional piezoelectric responses by four orders of magnitude.

Maximum polarization surpasses strain-induced piezoelectric limits.

Abstract

Piezoelectricity is a technologically important property of certain insulators in which mechanical strain induces an electrical polarization. However, the rate at which a piezoelectric response can be established over a macroscopic volume is limited by the sound velocity, constraining applications in high-bit-rate transduction and sensing. Furthermore, the strength of the piezoelectric effect is not readily tunable, as it depends on intrinsic anharmonic coupling between strain and intra-unit-cell distortions in a given material. Lastly, the maximum amplitude of the effect is bounded by material fracture, which sets in already at percent level strain values. Here we overcome these limitations by realizing a strain-free, piezoelectric-like response driven solely by photo-excited optical phonon distortions. We demonstrate such optical phonoelectricity in the weak piezoelectric BPO$_4$, in which we induce electrical polarization through phonon rectification. This effect is established over macroscopic volumes with four orders of magnitude higher speed than piezoelectric responses, ultimately limited by the speed of light. The maximum induced polarization is estimated to be far in excess of that attainable through strain at the fracture limit. Ultrafast phonoelectricity opens up new opportunities for optical control in quantum materials, but also for device applications.