Superconducting quantum interference device based on MgB2 nanobridges

The superconductor MgB2, with a transition temperature of 39 K, has significant potential for future electronics. An essential step is the achievement of Josephson circuits, of which the superconducting quantum interference device (SQUID) is the most important. Here, we report Josephson quantum interference in superconducting MgB2 thin films. Modulation voltages of up to 30 μV are observed in an all-MgB2 SQUID, based on focused-ion-beam patterned nanobridges. These bridges, with a length scale <100 nm, have outstanding critical current densities of 7×106 A/cm2 at 4.2 K.