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

## TL;DR

This paper reports on the development of vanadium-based superconducting quantum interference proximity transistors (SQUIPTs) that operate at higher temperatures, achieving high flux sensitivity and expanding potential applications in nanoscale sensing.

## Contribution

The study introduces fully superconducting V-based SQUIPTs with enhanced operating temperature up to 2 K and improved flux sensitivity, supported by a simplified theoretical model.

## Key findings

- Operate up to approximately 2 K, 70% higher than previous designs.
- Achieve flux-to-voltage up to 0.52 mV/Φ₀ and flux-to-current above 12 nA/Φ₀.
- Attain flux sensitivity of about 2.6 μΦ₀/√Hz under fixed voltage bias.

## Abstract

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$\ \textrm{mV}/\Phi_0$) and flux-to-current (above 12$\ \textrm{nA}/\Phi_0$) transfer functions, with the best estimated flux sensitivity $\sim$2.6$\ \mu\Phi_0/\sqrt{\textrm{Hz}}$ reached under fixed voltage bias, where $\Phi_0$ is the flux quantum. The interferometers operate up to $T_\textrm{bath}\simeq$ 2 $ \textrm{K}$, with an improvement of 70$\%$ 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.