HTS Josephson junctions as electromagnetic sensors for low and high frequencies

Josephson junctions are influenced by external electromagnetic fields in two ways. First, a time dependent vector potential changes the spatial phase distribution in the Josephson junction and leads to the observation of the magnetic field dependence of the critical current in the Fraunhofer pattern. In order to increase the dynamic range and to linearize such magnetic sensors flux-locked-loop operation can be employed with modulation frequencies up to the MHz-regime. Sensitive magnetometry with Josephson junctions allows the measurement of absolute magnetic fields with high spatial resolution. Josephson junctions from the high temperature superconductor (HTS) YBa2Cu3O7 and serial junction arrays for the measurement of magnetic fields are discussed.