Observation of spontaneous valley polarization of itinerant electrons

TL;DR

This paper demonstrates that in a two-dimensional electron system, valley polarization can be controlled via gate bias, driven by electron-electron interactions, leading to potential applications in valleytronic devices.

Contribution

It provides the first experimental demonstration of gate-tuned valley polarization driven by electron interactions in a simple 2D electron system.

Findings

Valley polarization switches from zero to one with small density reduction.

Sudden two-fold change in sample resistance at transition.

Observation of a gate-tuned, interaction-driven valley polarization transition.

Abstract

Memory or transistor devices based on electron's spin rather than its charge degree of freedom offer certain distinct advantages and comprise a cornerstone of spintronics. Recent years have witnessed the emergence of a new field, valleytronics, which seeks to exploit electron's valley index rather than its spin. An important component in this quest would be the ability to control the valley index in a convenient fashion. Here we show that the valley polarization can be switched from zero to one by a small reduction in density, simply tuned by a gate bias, in a two-dimensional electron system. This phenomenon arises fundamentally as a result of electron-electron interaction in an itinerant, dilute electron system. Essentially, the kinetic energy favors an equal distribution of electrons over the available valleys, whereas the interaction between electrons prefers single-valley occupancy below a critical density. The gate-bias-tuned transition we observe is accompanied by a sudden, two-fold change in sample resistance, making the phenomenon of interest for potential valleytronic transistor device applications. Our observation constitutes a quintessential demonstration of valleytronics in a very simple experiment.