Zero bias anomaly in Andreev reflection spectroscopy

Zero bias anomalies have been observed in point contact Andreev reflection spectroscopy using conventional superconductors, and they cannot be suppressed by a highly spin-polarized current. By systematically varying the size of the point contact, the anomalies are found to be evolved from conductance dips outside the superconducting gap. These anomalies, which depend on the size of the interface, are not intrinsic to the superconductors but due to a large resistance change when the contact region is driven to normal by an Oersted field.