Sodium impurities are diffused electrically to the oxide-semiconductor
interface of a silicon MOSFET to create an impurity band. At low temperature
and at low electron density, the band is split into an upper and a lower
sections under the influence of Coulomb interactions. We used
magnetoconductivity measurements to provide evidence for the existence of
Hubbard bands and determine the nature of the states in each band.Comment: In press in Physica