Spin-texture induced by oxygen vacancies in Strontium perovskites (001) surfaces: A theoretical comparison between SrTiO3 and SrHfO3

TL;DR

This study uses first-principles calculations to compare the effects of oxygen vacancies on the spin-texture and electronic properties of SrTiO3 and SrHfO3 (001) surfaces, revealing how atomic relaxations and spin-orbit coupling influence magnetism and electron gases.

Contribution

It provides a detailed theoretical comparison of oxygen vacancy effects on spin-texture and electronic structure in SrTiO3 and SrHfO3 surfaces, highlighting the role of spin-orbit interaction and structural relaxations.

Findings

Oxygen vacancies induce localized magnetic moments and 2D electron gases in SrTiO3.

Heavy Hf substitution enhances Rashba-like splitting due to larger spin-orbit coupling.

Magnetism and electron gas disappear in SrHfO3 after full structural optimization.

Abstract

The electronic structure of SrTiO3 and SrHfO3 (001) surfaces with oxygen vacancies is studied by means of first-principles calculations. We reveal how oxygen vacancies within the first atomic layer of the SrTiO3 surface (i) induce a large antiferrodistortive motion of the oxygen octahedra at the surface, (ii) drive localized magnetic moments on the Ti-3d orbitals close to the vacancies and (iii) form a two-dimensional electron gas localized within the first layers. The analysis of the spin-texture of this system exhibits a splitting of the energy bands according to the Zeeman interaction, lowering of the Ti-3dxy level in comparison with dxz and dyz and also an in-plane precession of the spins. No Rashba-like splitting for the ground state neither for ab-initio molecular dynamics trajectory at 400K is recognized as suggested recently by A. F. Santander-Syro et al. [1]. Instead, a sizeable Rashba-like splitting is observed when the Ti atom is replaced by a heavier Hf atom with a much larger spin-orbit interaction. However, we observe the disappearance of the magnetism and the surface two dimensional electron gas when full structural optimization of the SrHfO3 surface is performed. Our results uncover the sensitive interplay of spin-orbit coupling, atomic relaxations and magnetism when tuning these Sr-based perovskites.