Optical conductivity of a 2DEG with anisotropic Rashba interaction at the interface of LaAlO$_3$/SrTiO$_3$

TL;DR

This paper investigates the optical conductivity of a 2D electron gas with anisotropic Rashba spin-orbit interaction at LaAlO$_3$/SrTiO$_3$ interfaces, revealing unique features that differ from isotropic cases and can inform experimental analysis.

Contribution

It provides the first detailed analysis of optical conductivity in a 2DEG with anisotropic $k$-cubic Rashba interaction, highlighting distinctive spectral features and their implications.

Findings

Optical conductivity exhibits a single peak dependent on system parameters.

Charge and optical conductivities are isotropic despite anisotropic Fermi contours.

Infinitesimal photon energy can induce inter-band transitions due to degeneracy.

Abstract

We study optical conductivity of a two-dimensional electron gas with anisotropic $k$-cubic Rashba spin-orbit interaction formed at the LaAlO$_3$/SrTiO$_3$ interface. The anisotropic spin splitting energy gives rise to different features of the optical conductivity in comparison to the isotropic $k$-cubic Rashba spin-orbit interaction. For large carrier density and strong spin-orbit couplings, the density dependence of Drude weight deviates from the linear behavior. The charge and optical conductivities remain isotropic despite anisotropic nature of the Fermi contours. An infinitesimally small photon energy would suffice to initiate inter-band optical transitions due to degeneracy along certain directions in momentum space. The optical conductivity shows a single peak at a given photon energy depending on the system parameters and then falls off to zero at higher photon energy. These features are lacking for systems with isotropic $k$-cubic Rashba spin-orbit coupling. These striking features can be used to extract the information about nature of the spin-orbit interaction experimentally and illuminate some light on the orbital origin of the two-dimensional electron gas.