Why non-superconducting metallic elements become superconducting under high pressure

J.E. Hirsch and J.J. Hamlin, Physica C 470, S937 (2010), dx.doi.org/10.1016/j.physc.2009.10.093, cond-mat/0908.3496 (Los Alamos)

We predict that simple metals and early transition metals that become superconducting under high pressures will show a change in sign of their Hall coefficient from negative to positive under pressure. If verified, this will strongly suggest that hole carriers play a fundamental role in `conventional' superconductivity, as predicted by the theory of hole superconductivity.