Optimized proximity thermometer for ultrasensitive detection: Role of an ohmic electromagnetic environment

We propose a mesoscopic thermometer for ultrasensitive detection based on the proximity effect in superconductor-normal metal (SN) heterostructures. The device is based on the zero-bias anomaly due to the inelastic Cooper-pair tunneling in an SNIS junction (I stands for an insulator) coupled to an ohmic electromagnetic (EM) environment. The theoretical model is done in the framework of the quasiclassical Usadel Green's formalism and the dynamical Coulomb blockade. The usage of an ohmic EM environment makes the thermometer highly sensitive down to very low temperatures, T less than or similar to 5 mK. Moreover, defined in this way, the thermometer is stable against small but nonvanishing voltage amplitudes typically used for measuring the zero-bias differential conductance in experiments. Finally, we propose a simplified view, based on an analytic treatment, which is in very good agreement with numerical results and can serve as a tool for the development, calibration, and optimization of such devices in future experiments in quantum calorimetry.

Automated summary

A mesoscopic thermometer for ultrasensitive detection based on the proximity effect in superconductor-normal metal (SN) heterostructures is proposed. The thermometer utilizes the zero-bias anomaly caused by inelastic Cooper-pair tunneling in an SNIS junction coupled to an ohmic electromagnetic environment. A simplified analytic treatment is also proposed, which agrees well with numerical results and can be used for the development, calibration, and optimization of such devices in future experiments.