Observation of large h/2e and h/4e oscillations in a proximity dc superconducting quantum interference device

We have measured the magnetoresistance of a dc superconducting quantum interference device in the form of an interrupted mesoscopic normal metal loop in contact with two superconducting electrodes. Below the transition temperature of the superconducting electrodes, large h2e periodic magnetoresistance oscillations are observed. By adding a small dc bias to the ac measurement current, h4e oscillations can be produced. Lowering the temperature further leads to even larger oscillations, and eventually to sharp switching from the superconducting state to the normal state. This flux-dependent resistance could be utilized to make a highly sensitive flux detector.