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 ΔC/γT c = 1.43, while the superconducting gap Δ(0) is 0.92 meV, precisely matching the theoretical prediction of the weak-coupling Bardeen–Cooper–Schrieffer 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 MEAs and HEAs superconductors but also open new avenues for the development of superconductors with ultralow magnetic relaxation rates.