Analysis of electric-field-induced spin splitting in wide modulation-doped quantum wells

TL;DR

This paper examines how electric fields influence spin splitting in wide quantum wells, emphasizing a multiband approach for accurate modeling and demonstrating a method to control Rashba splitting with smaller electric fields.

Contribution

It introduces a multiband framework for including electric-field-induced spin splittings and shows how to effectively switch Rashba splitting on and off with smaller electric fields.

Findings

Multiband approach provides a more accurate inclusion of Rashba effect.

Electric field can control Rashba splitting efficiently.

Implications for spintronic device design, especially spin transistors.

Abstract

We analyze the proper inclusion of electric-field-induced spin splittings in the framework of the envelope function approximation. We argue that the Rashba effect should be included in the form of a macroscopic potential as diagonal terms in a multiband approach rather than the commonly used Rashba term dependent on k and electric field. It is pointed out that the expectation value of the electric field in a subband is sometimes not unique because the expectation values can even have opposite signs for the spin-split subband components. Symmetric quantum wells with Dresselhaus terms and the influence of the interfaces on the spin splitting are also discussed. We apply a well established multiband approach to wide modulation-doped InGaSb quantum wells with strong built-in electric fields in the interface regions. We demonstrate an efficient mechanism for switching on and off the Rashba splitting with an electric field being an order of magnitude smaller than the local built-in field that determines the Rashba splitting. The implications of our findings for spintronic devices, in particular the Datta-Das spin transistor and proposed modifications of it, are discussed.