Evaporation and quantum tunneling of electrons from a helium surface

We have measured the escape rate of electrons from two-dimensional surface states of bulk helium. These measurements were made through a range of densities, external field, and temperature where thermal activation dominates (T≥0.6 K) into the range where quantum tunneling dominates (T≤0.6 K). Both processes are sensitive to electron-electron correlation effects. The thermal activation rates depend only on the barrier height for which a relatively simple approximation of the correlation is adequate. However, observed tunneling rates are many orders of magnitude greater than would be predicted by this same approximation.