Theory of Rashba splitting in quantum-well states

TL;DR

This paper develops a first-principles theory for Rashba energy splitting in quantum-well states, deriving a linear Rashba term and analyzing its behavior using a tight-binding model validated by realistic system data.

Contribution

It introduces a novel derivation of the Rashba term from first principles and applies a tight-binding model to analyze Rashba splitting in quantum wells.

Findings

The Rashba splitting can be analytically expressed as a function of monolayer number and well depth.

The tight-binding model qualitatively matches first-principles results with only two fitting parameters.

The theory predicts conditions for maximizing Rashba splitting in quantum wells.

Abstract

We present a theory pertaining to the asymptotic behavior of Rashba energy splitting in a quantum-well state (QWS). First, unlike previous studies, we derive $\textbf{k}$-linear Rashba term from a first-principles Hamiltonian in a physically convincing manner. The $\textbf{k}$-dependent in-plane intrinsic magnetic-field term originates from the spin--orbit interaction and hybridized $s$-$p_z$ orbital, whereas a steep nucleus potential realizes the linearity for the $\textbf{k}$ of the effective magnetic field. Next, we analyze the Rashba effect of a QWS using a one-dimensional tight-binding model developed based on the bottom-up approach that is aforementioned. The Rashba-splitting behavior of this system is captured from the density at the interface. The density can be expressed analytically as a function of the monolayer number and well depth. Finally, we apply our formula to the QWS of a few-monolayers Ag on an Au(111) surface to validate the theory based on a realistic system. Our tight-binding analysis qualitatively fits the first-principles result using only two fitting parameters and predicts the optimal condition for achieving a large Rashba splitting.