Quantal Andreev billiards: Density of states oscillations and the spectrum-geometry relationship

Andreev billiards are finite, arbitrarily shaped, normal-state regions, surrounded by superconductor. At energies below the superconducting energy gap, single-quasiparticle excitations are confined to the normal region and its vicinity, the mechanism for confinement being Andreev reflection. Short-wave quantal properties of these excitations, such as the connection between the density of states and the geometrical shape of the billiard, are addressed via a multiple scattering approach. It is shown that one can, inter alia, ‘‘hear’’ the stationary chords of Andreev billiards.