Thermodynamics of the hydrogen dominant potassium hydride superconductor at high pressure

Author-Highlights
• The superconducting state in hydrogen dominant potassium hydride superconductor is examined.
• The Eliashberg formalism is used to determine the thermodynamic properties.
• The observed thermodynamic properties strongly deviate from the BCS predictions.

In the present paper we report comprehensive analysis of the thermodynamic properties of novel hydrogen dominant potassium hydride superconductor (KH6). Our computations are conducted within the Eliashberg theory which yields quantitative estimations of the most important thermodynamic properties of superconducting phase. In particular, we observe that together with the increasing pressure all the thermodynamic properties decrease, e.g.  TC∈〈72.91,55.50〉TC∈〈72.91,55.50〉 K for p∈〈166,300〉p∈〈166,300〉 GPa. It is predicted that such decreasing behavior corresponds to the decreasing hydrogen lattice molecularization with increasing pressure value. Furthermore, by calculating the dimensionless thermodynamic ratios, familiar in the Bardeen–Cooper–Schrieffer (BCS) theory, it is proved that KH6 material is a strong-coupling superconductor and cannot be quantitatively described within the BCS theory.