Anisotropy of the Characteristic Critical Fields and Length Scales of Sr_{1 − <i>x</i>}K_<i>x</i>Fe₂As₂ Superconductor

Abstract In the current research work, the anisotropy of the characteristic critical fields and length scales of Sr 1 − x K x Fe 2 As 2 superconductor by employing the Ginzburg–Landau (GL) phenomenological free energy density functional theory is investigated. Using this model, mathematical expressions are obtained that describe the temperature dependence of the lower, thermodynamic, and upper critical magnetic fields parallel and perpendicular to the c‐axis, the GL characteristic parameter, the GL coherence length and GL penetration depth, and the angular dependence of the upper critical magnetic field. Using these mathematical expressions, phase diagrams are plotted using Matplotlib in Python. These phase diagrams show that the characteristic critical magnetic fields—the lower, thermodynamic, and upper critical magnetic fields (both parallel and perpendicular to the c‐axis)—and the GL characteristic parameter decrease with increasing temperature and vanish at the superconducting critical temperature (T C ), T C = 37 K for Sr 1 − x K x Fe 2 As 2 superconductor. On the other hand, the characteristic length scales—the GL coherence length and GL penetration depth—increase with temperature and diverge at 37 K. The upper critical magnetic field varies with angle (θ). The findings also reveal the anisotropic properties of the lower and upper critical magnetic fields of Sr 1 − x K x Fe 2 As 2 superconductors.