Spin and the Coulomb gap in the half-filled lowest Landau level

In a strong magnetic field, two-dimensional electron systems are dominated by Coulomb interactions between the electrons. While the most familiar manifestation of these interactions is the fractional quantum Hall effect, this is actually a relatively subtle variation in the strong electronic correlations that exist throughout the high-field regime. This is clearly revealed in tunneling experiments in which an uncorrelated electron is rapidly thrust into a strongly correlated electron gas. A robust Coulomb pseudogap is observed, with tunneling strongly suppressed until the energy of the incoming electron is large enough. The Coulomb gap is insensitive to the precise magnetic field and is typically much larger than the energy gap associated with the fractional quantum Hall effect. In the present paper, the authors demonstrate that the size of the Coulomb gap observed in tunneling between two parallel two-dimensional electron systems depends sensitively on their spin configuration, with larger gaps associated with a larger net spin polarization. In effect, it is easier for electrons `to get out of the way' of an incoming tunneling electron when the spin polarization of the electron gas is less than complete.