2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/27500A theory is presented for the statistics of the excitation spectrum of a disordered metal grain in contact with a superconductor. A magnetic field is applied to fully break time-reversal symmetry in the grain. Still, an excitation gap of the order of $δ$ opens up provided $NΓ^2\gtrsim 1$. Here $δ$ is the mean level spacing in the grain, $Γ$ the tunnel probability through the contact with the superconductor, and $N$ the number of transverse modes in the contact region. This provides a microscopic justification for the new random-matrix ensemble of Altland and Zirnbauer.4 pages, 2 figures, to appear in Phys. Rev. LettCondensed Mattertext