One of the most far-reaching problems in condensed-matter physics is to und
erstand how interactions between electrons, and the resulting correlations,
affect the electronic properties of disordered two-dimensional systems. Ex
tensive experimental (1-6) and theoretical (7-11) studies have shown that i
nteraction effects are enhanced by disorder, and that this generally result
s in a depletion of the density of electronic states. In the limit of stron
g disorder, this depletion takes the form of a complete gap(12,13) in the d
ensity of states. It is known that this `Coulomb gap' can turn a pure metal
film that is highly disordered into a poorly conducting insulator(14), but
the properties of these insulators are not well understood. Here we invest
igate the electronic properties of disordered beryllium films, with the aim
of disentangling the effects of the Coulomb gap and the underlying disorde
r. We show that the gap is suppressed by a magnetic field and that this dri
ves the strongly insulating beryllium films into a low-temperature `quantum
metal' phase with resistance near the quantum resistance R-Q = h/e(2), whe
re h is Planck's constant and e is the electron charge.