Abstract
A new thermometric method is proposed in the liquid helium temperature region with reference temperature determined by the super-to-normal (S-N) transition of a superconductor. This method is expected to be superior, with further improvements, to conventional ones in the sensitivity, reproducibility and response speed, which can be enhanced by the sharp and dependable S-N transition and by the thin film structure of its sensor.
A superconductor thin film immersed in liquid helium of temperature (TB) lower than its transition temperature can be kept at its transition temperature (TC) by introducing a thermal feedback controller operating on (TC-TB). The amount of this thermal feedback gives a thermometric measure from TC. In the vicinity of TC, the heat generated by this thermal feedback can be minimized to a degree negligible in almost all practical situations.
A practical sensor trially manufactured by the authors has a double layer structure: one layer is an Sn film as a superconductive material and the other layer a nichrome film as a thermal feedback element. This setup works between 2.78 and 3.64K giving an output monotonically related to the temperature difference.
This paper presents just the working principle of the new method and its experimental verification. Practical improvements are left for the future study.
