Observation of spontaneous valley polarization of itinerant electrons

Md. S. Hossain, M. K. Ma, K. A. Villegas Rosales, Y. J. Chung, \Ł. N. Pfeiffer, K. W. West, K. W. Baldwin, M. Shayegan

Published 2020-11-13Version 1

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 \cite{Zutic.RMP.2004}. 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.