Valleytronics is rapidly emerging as an exciting area of basic and applied research. In two-dimensional systems, valley polarization 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 polarization. In stark contrast to expectations from a non-interacting model, we show experimentally that less magnetic field can be required to fully spin polarize a valley-polarized 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 crystalization, which in turn suggests the existence of a new strongly correlated electron liquid at low electron densities.

We examine the electron mobility and hole mobility at the Si/buried oxide (BOX) interface at which the valley splitting of the electron system is strongly enhanced, and compare the values observed to those at a standard Si/thermal oxide (T-SiO2) interface in the same silicon-on-insulator device. In contrast to the electron mobility, which is lower at the Si/BOX interface, the hole mobility at the Si/BOX interface is found to be slightly higher than that at the Si/T-SiO2 interface.

We examine the temperature dependence of resistivity in a two-dimensional electron system formed in a silicon-on-insulator quantum well. The device allows us to tune the valley splitting continuously in addition to the electron density. Our data provide a global picture of how the resistivity and its temperature dependence change with valley polarization. At the boundary between valley-polarized and partially polarized regions, we demonstrate that there is an insulating contribution from spin-degenerate electrons occupying the upper valley-subband edge.

We demonstrate that spin polarization and valley polarization have quantitatively similar effects on the resistivity of a two-dimensional electron gas in a silicon-on-insulator quantum well. In-sodoing, we also examine the dependence on disorder, leading to a coarse but global phenomenology of how the resistivity depends on its key parameters: spin-and valley-polarization, density, disorder and temperature.