Geometry-specific conductance fluctuations in semiconductor-superconductor microjunctions

The conductance of quantum dots contacted to a superconductor is found to exhibit geometry-specific fluctuations in low magnetic fields. In particular, the conductance fluctuations in a rectangular-shaped quantum dot develop hierarchical structures around zero magnetic field. The fluctuations are drastically suppressed when the lead is attached to the corner of the dot. These observations demonstrate significant modifications of the quantum interference effects by Andreev reflections. In addition, the self-similarity of the conductance fluctuations does not necessarily guarantee the underlying classical dynamics to be chaotic.