High operating temperature in V-based superconducting quantum interference proximity transistors

Here we report the fabrication and characterization of fully superconducting quantum interference proximity transistors (SQUIPTs) based on the implementation of vanadium (V) in the superconducting loop. At low temperature, the devices show high flux-to-voltage (up to 0.52$\text{ mV}\mathrm{/}{\mathrm{\Phi }}_0$) and flux-to-current (above 12$\text{ nA}\mathrm{/}{\mathrm{\Phi }}_0$) transfer functions, with the best estimated flux sensitivity $\sim$2.6$\mu {\mathrm{\Phi }}_0\mathrm{/}\sqrt{\text{Hz}}$ reached under fixed voltage bias, where ${\mathrm{\Phi }}_0$ is the flux quantum. The interferometers operate up to $T_{\text{bath}}\simeq$ 2 $\text{K}$, with an improvement of 70$\mathrm{\%}$ of the maximal operating temperature with respect to early SQUIPTs design. The main features of the V-based SQUIPT are described within a simplified theoretical model. Our results open the way to the realization of SQUIPTs that take advantage of the use of higher-gap superconductors for ultra-sensitive nanoscale applications that operate at temperatures well above 1 K.