# Activation of nominally silent domain wall-localized phonons from GHz to THz frequencies

## TL;DR

This paper reveals that ferroelectric domain walls host phonons from GHz to THz frequencies, explaining their broad GHz conductivity signature and enabling new nanophononic device designs.

## Contribution

It uncovers the broad frequency range of DW phonons and explains the activation of silent modes due to wall tilting, advancing understanding of DW nanophononics.

## Key findings

- DW phonons disperse from GHz to THz frequencies
- Activation of silent DW modes is due to wall tilting and asymmetry
- Simulations predict scanning impedance microscopy as a probe

## Abstract

Ferroelectric domain walls (DWs) are nanoscale topological defects that can be easily tailored to create nanoscale devices. Their excitations, recently discovered to be responsible for DW GHz conductivity, hold promise for faster signal transmission and processing speed compared to the existing technology. Here we find that DW phonons disperse from GHz to THz frequencies, thus explaining the origin of the surprisingly broad GHz signature in DW conductivity. Puzzling activation of nominally silent DW sliding modes in BiFeO3 is traced back to DW tilting and resulting asymmetry in wall-localized phonons. The obtained phonon spectra and selection rules are used to simulate scanning impedance microscopy, emerging as a powerful probe in nanophononics. The results will guide experimental discovery of the predicted phonon branches and design of DW-based nanodevices.