Strong Spin-Orbit Interaction and Helical Hole States in Ge/Si Nanowires

TL;DR

This paper theoretically investigates Ge/Si nanowires, revealing strong spin-orbit interaction and helical hole states that enable electrical spin control, with tunable energy levels suitable for quantum dot and qubit applications.

Contribution

It demonstrates the presence of large Rashba-type spin-orbit coupling and helical states in Ge/Si nanowires, controlled by shell thickness and external fields, advancing spin qubit technology.

Findings

Large Rashba spin-orbit interaction (~meV) in Ge/Si nanowires.

Control of low-energy hole states via shell thickness and electric fields.

Potential for quantum dots and spin qubits with tunable energy levels.

Abstract

We study theoretically the low-energy hole states of Ge/Si core/shell nanowires. The low-energy valence band is quasidegenerate, formed by two doublets of different orbital angular momenta, and can be controlled via the relative shell thickness and via external fields. We find that direct (dipolar) coupling to a moderate electric field leads to an unusually large spin-orbit interaction of Rashba type on the order of meV which gives rise to pronounced helical states enabling electrical spin control. The system allows for quantum dots and spin qubits with energy levels that can vary from nearly zero to several meV, depending on the relative shell thickness.