Unveiling intrinsic Superconductivity in HfNbZrTi Medium-Entropy Alloy Single Crystals

Abstract Medium and high entropy alloys (MEAs and HEAs) have emerged as promising materials in materials science and engineering, offering exceptional mechanical properties and intriguing low-temperature physical characteristics. In the study of superconducting mechanisms, high-quality, large single crystals are essential for obtaining reliable experimental data. Here, we report the first successful growth of high-quality MEA HfNbZrTi single crystals using the Floating Zone Method and present a comprehensive investigation of their superconducting properties, vortex dynamics, and specific heat. Notably, the specific heat jump extracted from experimental data yields ∆C/γTc = 1.43, while the superconducting gap Δ(0) is 0.92 meV, precisely matching the theoretical prediction of the weak-coupling BCS model. Furthermore, we report the first investigation of magnetic relaxation in MEA single crystals, revealing an exceptionally low relaxation rate (S < 0.02 at 2 K). These findings not only provide strong experimental evidence supporting the application of medium- and high-entropy alloy superconductors but also open new avenues for the development of superconductors with ultralow magnetic relaxation rates.