A four-junction switch for controlling the opening and closing of a pickupcoil in high-T-c superconducting quantum interference device magnetometer

We study a method to prevent thermally activated flux entry through a flux dam in a high-T-c superconducting quantum interference device (SQUID) magne tometer. For this purpose. the circulating current flowing in a pickup loop of the magnetometer must be much below the critical current of the flux da m. In order to forcibly reduce the circulating current due to a residual ma gnetic field, we propose a switch consisting of four bicrystal junctions, i nstead of the conventional flux dam. Using the switch, we can electrically control the opening and closing of the pickup loop, and therefore, can redu ce the circulating current to zero. The usefulness of the switch is demonst rated.