Stripe charge ordering in SrO-terminated SrTiO3(001) surfaces

TL;DR

This study reveals charge-ordered stripe patterns on SrO-terminated SrTiO3(001) surfaces caused by oxygen vacancy doping, with localized in-gap states indicating strong electron-lattice interactions.

Contribution

It provides direct STM evidence of charge ordering and electron-lattice coupling on SrTiO3 surfaces, a novel insight into surface electronic structure.

Findings

Unidirectional 3-unit-cell periodicity along the a axis

Charge-ordered stripe induced by oxygen vacancies

Localized in-gap states with large energy gaps

Abstract

The local electronic structure of the SrO-terminated SrTiO3(001) surface was explored using scanning tunneling microscopy. At low bias voltages in the empty states, a unidirectional structure with a periodicity of 3 unit cells, superimposed on a c(2 x 2) reconstructed structure, was found to develop along the crystallographic a axis. This structure indicates a charge-ordered stripe induced by carrier doping from oxygen vacancies in the SrO and the subsurface TiO2 planes. In the filled states, localized deep in-gap states were observed in addition to large energy gaps in the tunneling spectra. This result represents inelastic tunneling due to significant electron-lattice interaction associated with unidirectional lattice distortion in the SrO-terminated surface.