VTT quantum-Hall setup

The authors present a compact setup for quantum Hall measurements consisting of an overlapped-tube cryogenic current comparator, where the imbalance is detected with a sensitive DC-SQUID (superconducting quantum interference device) magnetometer, and a small superconducting magnet system operated in a standard liquid-helium storage dewar. The system also incorporates PC-controlled electronics, which facilitates automatic measurements. The setup has been developed for a small-scale national standards laboratory where resistance calibrations at an uncertainty level of 10/sup -8/ are performed. A block diagram of the electronics of the measurement setup is shown along with a 1.5 K insert that includes a complete superconducting magnet system and the quantum-Hall probe.<>