International Journal of Physics | Vol. 17, No. 8, August 2026 | pp. 105–112
DOI: 10.46882/2026/IJP/000202
Research Article
Title: Superconducting Critical Fields and Upper Phase Boundaries of Iron-Chalcogenide Single Crystals
Names of Authors: K. A. Tanaka¹, V. N. Volkov², S. C. Williams³
Authors’ Affiliations:
¹ Department of Physics, Tokyo Institute of Technology, Tokyo, Japan
² Kapitza Institute for Physical Problems, Russian Academy of Sciences, Moscow, Russia
³ Clarendon Laboratory, Department of Physics, University of Oxford, Oxford, UK
Abstract: Iron-based superconductors attract intense interest due to their high critical fields and unconventional pairing mechanisms. We synthesized high-quality single crystals of the iron-chalcogenide superconductor FeSe0.4Te0.6 using a self-flux crystal growth technique. The superconducting properties and phase diagram were investigated via temperature-dependent electrical resistivity and magnetic susceptibility measurements under high DC magnetic fields up to 16.0 T. The pristine single crystals showed a sharp superconducting transition with a critical temperature (Tc) of 14.5 K at zero magnetic field. The transition width was exceptionally narrow at dT = 0.4 K, indicating excellent chemical homogeneity. When an external magnetic field was applied parallel to the crystal ab-plane, the upper critical field, Hc2(0), was estimated to be 48.2 T by applying the Werthamer-Helfand-Hohenberg (WHH) theoretical model. Conversely, with the magnetic field aligned parallel to the c-axis, Hc2(0) dropped to 26.8 T. This response yields an anisotropy factor of approximately Gamma = 1.80 near the transition temperature. The temperature dependence of Hc2 along both crystallographic axes exhibits a distinct linear upward curvature. This behaviour deviates significantly from conventional single-band WHH predictions and strongly implies a multiband superconductivity mechanism. Magnetization loops revealed a high critical current density (Jc) exceeding 2.5 x 10⁵ A/cm² at 4.2 K under zero field. This high current capacity underscores the potential of FeSe0.4Te0.6 single crystals for high-field engineering applications.
Keywords: Iron-based superconductors; Single crystal growth; Upper critical field; Multiband superconductivity; Magnetoresistance; Anisotropy factor
Manuscript Timeline: Received: June 04, 2026 / Revised: July 08, 2026 / Accepted: July 28, 2026 / Published: August 14, 2026
Citation: Tanaka, K. A., Volkov, V. N., & Williams, S. C. (2026). Superconducting Critical Fields and Upper Phase Boundaries of Iron-Chalcogenide Single Crystals. International Journal of Physics, 17(8), 105–112.
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