Valley splitting in a Si/SiGe quantum point contact

TL;DR

This paper combines theoretical modeling and experimental measurements to analyze valley splitting in a Si/SiGe quantum point contact, revealing how confinement and interface steps influence valley splitting magnitude.

Contribution

It introduces a comprehensive effective mass theory for QPCs in Si/SiGe heterostructures and demonstrates the impact of magnetic and quantum confinement on valley splitting.

Findings

Valley splitting increases with magnetic and quantum confinement.

Different transverse modes exhibit varying valley splittings.

Interface steps significantly influence valley splitting magnitude.

Abstract

We present the theory and measurement of valley splitting in a quantum point contact (QPC) in a modulation doped Si/SiGe heterostructure. Our measurements are performed on a submicron Schottky-gated device. An effective mass theory is developed for a QPC formed in a quantum well, grown on a miscut substrate. Both theory and experiments include a perpendicular magnetic field. Our results indicate that both QPC and magnetic confinement can enhance the valley splitting by reducing the spatial extent of the electronic wavefunction. Consequently, the valley splitting can be much larger than the spin splitting for small magnetic fields. We also observe different valley splittings for different transverse modes in the QPC, supporting the notion that when steps are present at the quantum well interface, the spatial extent of the wavefunction plays a dominant role in determining the valley splitting.