Valley polarization assisted spin polarization in two dimensions

TL;DR

This paper demonstrates that valley polarization in two-dimensional silicon quantum wells enhances spin polarization at lower magnetic fields, revealing strong electron correlations and a potential new electron liquid state.

Contribution

It provides experimental evidence and theoretical modeling showing valley polarization reduces the magnetic field needed for full spin polarization in 2D systems, highlighting strong correlations.

Findings

Less magnetic field needed for spin polarization in valley-polarized systems

Quantitative agreement with ab initio quantum Monte Carlo simulations

Indication of a new strongly correlated electron liquid state

Abstract

Valleytronics is rapidly emerging as an exciting area of basic and applied research. In two dimensional systems, valley polarisation can dramatically modify physical properties through electron-electron interactions as demonstrated by such phenomena as the fractional quantum Hall effect and the metal-insulator transition. Here, we address the electrons' spin alignment in a magnetic field in silicon-on-insulator quantum wells under valley polarisation. In stark contrast to expectations from a non-interacting model, we show experimentally that less magnetic field can be required to fully spin polarise a valley-polarised system than a valley-degenerate one. Furthermore, we show that these observations are quantitatively described by parameter free ab initio quantum Monte Carlo simulations. We interpret the results as a manifestation of the greater stability of the spin and valley degenerate system against ferromagnetic instability and Wigner crystalisation which in turn suggests the existence of a new strongly correlated electron liquid at low electron densities.