Valley Polarization in Si(100) at Zero Magnetic Field

The valley splitting, which lifts the degeneracy of the lowest two valley states in a SiO$_2$/(100)Si/SiO$_2$ quantum well is examined through transport measurements. We demonstrate that the valley splitting can be observed directly as a step in the conductance defining a boundary between valley-unpolarized and polarized regions. This persists to well above liquid helium temperature and shows no dependence on magnetic field, indicating that single-particle valley splitting and valley-polarization exist in (100) silicon even at zero magnetic field.