SQUID-based high-resolution thermometer

High-resolution thermometers (HRTs) based on the detection of magnetization changes of a magnetic material using very sensitive superconducting quantu m interference device (SQUID) have routinely achieved temperature resolutio n of 0.1 nK/root Hz at temperatures below 4 K in several laboratories. The resolution of these thermometers has reached the fundamental limit imposed by thermodynamic fluctuations. The principle of operation as well as the th eory of the noise are presented. Some recent discoveries using HRT are disc ussed. (C) 2001 Elsevier Science Ltd. All rights reserved.