  We report on the tunneling density of states (DOS) in ultrathin and strongly
disordered Be films quench-condensed at 20 K. Above 5 K, the DOS shows the
well-known logarithmic anomaly at the Fermi level. Only in a narrow temperature
range near 2 K is the DOS linearly dependent on energy, as predicted by Efros
and Shklovskii. However, both the zero-bias conductance and the slope of the
linear DOS are found to decrease drastically with decreasing temperature.
Tunneling measurements at mK temperatures have revealed conclusively that a
hard correlation gap opens up in the DOS.
