Tunable spin and orbital polarization in SrTiO3-based heterostructures

TL;DR

This paper develops an analytical model for Rashba spin-orbit coupling in LaAlO3/SrTiO3 heterostructures, revealing how tunable parameters influence spin and orbital properties, with results aligning with experiments.

Contribution

It provides explicit formulas linking heterostructure parameters to Rashba spin-orbit coupling and orbital effects, advancing understanding of tunable spin phenomena in oxide interfaces.

Findings

Linear RSOC dominates near the Γ-point.

Cubic RSOC becomes significant at higher energies.

RSOC strength depends strongly on heterostructure parameters.

Abstract

We formulate the effective Hamiltonian of Rashba spin-orbit coupling (RSOC) in $\mathrm{LaAlO_3/SrTiO_3}$ (LAO/STO) heterostructures. We derive analytical expressions of properties, e.g., Rashba parameter, effective mass, band edge energy and orbital occupancy, as functions of material and tunable heterostructure parameters. While linear RSOC is dominant around the $\Gamma$-point, cubic RSOC becomes significant at the higher-energy anti-crossing region. We find that linear RSOC stems from the structural inversion asymmetry (SIA), while the cubic term is induced by both SIA and bulk asymmetry. Furthermore, the SOC strength shows a striking dependence on the tunable heterostructure parameters such as STO thickness and the interfacial electric field which is ascribed to the quantum confinement effect near the LAO/STO interface. The calculated values of the linear and cubic RSOC are in agreement with previous experimental results.