Observation of Wannier-Stark localization at the surface of BaTiO$_3$ films by photoemission

TL;DR

This study demonstrates the direct observation of Wannier-Stark localization at the surface of ferroelectric BaTiO₃ films using photoemission, revealing localized surface states influenced by intrinsic electric fields.

Contribution

First direct experimental evidence of Wannier-Stark localization at a ferroelectric surface using angle-resolved photoemission spectroscopy.

Findings

Wannier-Stark localized surface states observed at BaTiO₃ interface

Localization extends to SrTiO₃ overlayers

Electrons localized along in-plane polarization direction

Abstract

Observation of Bloch oscillations and Wannier-Stark localization of charge carriers is typically impossible in single-crystals, because an electric field higher than the breakdown voltage is required. In BaTiO$_3$ however, high intrinsic electric fields are present due to its ferroelectric properties. With angle-resolved photoemission we directly probe the Wannier-Stark localized surface states of the BaTiO$_3$ film-vacuum interface and show that this effect extends to thin SrTiO$_3$ overlayers. The electrons are found to be localized along the in-plane polarization direction of the BaTiO$_3$ film.