# Nanoscale symmetry protection of the reciprocal acoustoelectric effect

## TL;DR

The paper explores how symmetry at the nanoscale protects reciprocal acoustoelectric effects in surface acoustic wave configurations.

## Contribution

The study experimentally identifies symmetry-based protection mechanisms for reciprocal acoustoelectric effects at the nanoscale.

## Key findings

- Reciprocal acoustoelectric effects are preserved in half of the surface acoustic wave configurations due to symmetry elements.
- The other half lacks direct symmetry but relates to the first through directional interchange of wave propagation.
- Symmetry in the equation of motion explains the correspondence between these configurations at nanoscale distances.

## Abstract

Neumann’s principle states that all physical properties of a material are bound by its symmetry. While bulk crystals conform to well-defined point and space groups, phenomena at a substrate’s surface could have less apparent symmetry origins. Here we experimentally explore both reciprocal and non-reciprocal types of acoustoelectric effects driven by surface acoustic waves (SAW). The non-reciprocal acoustoelectric voltage is connected to the natural single-phase unidirectional transducer from device engineering. On the other hand, reciprocal acoustoelectric effect exists in certain SAW configurations that are of different symmetry origins. Half of the configurations have a valid reciprocity-preserving symmetry element of either a mirror plane or a two-fold rotational axis that is perpendicular to the substrate surface. The other half of the configurations do not possess a reciprocity-preserving symmetry element of the half-space but relate to the first scenario through an interchange of SAW propagation and the surface normal directions. Here, it is the symmetric construction in the equation of motion, which holds at nanoscale distances, to be responsible for the correspondence between two scenarios and extends the cases of reciprocal SAW states. This correspondence traces its physical origin to the SAW composition of compression and shear waves along two orthogonal directions respectively.

The online version contains supplementary material available at 10.1038/s41598-026-38987-6.