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 $h/2e$ periodic magnetoresistance oscillations are observed. By adding a small dc bias to the ac measurement current, $h/4e$ 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 highly sensitive flux detector.