Pressure effects on the superconductivity in FeH[formula omitted] compound

Abstract

Recent investigations on the existence of a superconducting state in hydrogen dominant compounds containing iron show the advantage of chemical precompression. This procedure allows decreasing pressure needed to metalize hydrogen comparing to pristine structure, preserving exceptional superconducting properties. This work comprises a study on the thermodynamic properties of the superconducting state in FeH5 compound in stable I4/mmm symmetry form. Using the formalism of strong coupling Eliashberg theory of superconductivity, the thermodynamic quantities of critical temperature, free energy, entropy, and specific heat difference have been investigated on the quantitative level. Results show the downward trend of transition temperature obtained for three different pressure values ensuring I4/mmm structure, namely 150 GPa, 200 GPa, 300 GPa (51 K, 45 K, 43 K, respectively, for μ⋆ = 0.1). The above tendency affects the rest of the thermodynamic properties of the superconducting state, thus FeH5 pressurized to 150 GPa reveals the best characteristics compared to higher values. Critical temperatures obtained within the framework of this paper significantly exceed the predictions of Allen–Dynes and McMillan analytic formulas. Furthermore, BCS theory coefficients RΔ, RH, RC diverge remarkably from their standard values, implying the requirement to use the Eliashberg approach for proper superconducting state description.