Andreev Conductance of Chaotic and Integrable Quantum Dots

We examine the voltage V and magnetic field B dependent Andreev conductance of a chaotic quantum dot coupled via point contacts to a normal metal and a superconductor. In the case where the contact to the superconductor dominates, we find that the conductance is consistent with the dot itself behaving as a superconductor-- it appears as though Andreev reflections are occurring locally at the interface between the normal lead and the dot. This is contrasted against the behaviour of an integrable dot, where for a similar strong coupling to the superconductor, no such effect is seen. The voltage dependence of the Andreev conductance thus provides an extremely pronounced quantum signature of the nature of the dot's classical dynamics. For the chaotic dot, we also study non-monotonic re-entrance effects which occur in both V and B.