Hard correlation gap observed in quench-condensed ultrathin beryllium - art. no. 036801

We report on the tunneling density of states (DOS) in strongly disordered u ltrathin Be films quench condensed at 20 K. Above 5 K, the DOS shows the we ll-known logarithmic anomaly at the Fermi level. Only in a narrow temperatu re 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 temper ature. Tunneling measurements at mK temperatures have revealed conclusively that a hard correlation gap opens up in the DOS.