Hall Sensor Based Measurements of the Magnetic Phase Diagram of Superconducting Vanadium

Abstract

Vanadium is an elemental type-II superconductor which has a pure superconducting phase, a vortex phase, and a non-superconducting phase. We designed and carried out a low-budget experiment in our undergraduate physics lab to measure the magnetic field a close distance from the surface of a pure Vanadium disk sample isothermally with a Hall sensor across a range of different temperatures and external magnetic fields. We then used these measurements to compute the superconducting phase diagram of Vanadium. After completing measurements at eight temperatures ranging from 2.6K to 5K and magnetic fields ranging from -0.2T to 0.2T, we were able to detect the Meissner phase (clearly), and a vortex phase (less clearly). Using the graphs of the hall bar magnetic field versus external magnetic field, we were able to derive a rough estimate for the upper critical field and the lower critical field of Vanadium at the eight temperatures wherein we conducted measurements. The results are in general accord with the phase diagram of Vanadium found in the literature, except that the critical temperature appears to be less than 5.43K and 5.13K (about 4.8K). Further, we observed critical fields lower than those found in the literature. We hypothesize this is due mostly to impurities in our Vanadium sample (purchased through Amazon.com), which would reduce the measured critical temperature below that of pure Vanadium, consistent with our results.