Thermodynamic investigations of high-pressure superconducting state in CaLi2 at 45 GPa

The thermodynamic properties of the high-pressure superconducting phase in CaLi2 have been studied. A pressure value of 45 GPa has been chosen, at which the critical temperature reaches the maximum (TC=12.9K). The following results have been obtained. (i) The critical temperature cannot be calculated using the classical analytical formulas (McMillan or Allen–Dynes). (ii) The critical value of the Coulomb pseudopotential is high: μC⋆=0.23. Generalizing the results, the function μC⋆(p) has a high value (μC⋆(p)>0.15) in practically the entire pressure range from 28 to 60 GPa. (iii) The remaining fundamental thermodynamic parameters differ from the Bardeen, Cooper, and Schrieffer (BCS) values. In particular, the zero-temperature energy gap to the critical temperature: R1≡2Δ(0)/kBTC=3.95R1≡2Δ(0)/kBTC=3.95; the ratio of the specific heat for superconducting (CSCS) and the normal (CNCN) state: R2≡(CS(TC)−CN(TC))/CN(TC)=2.01R2≡(CS(TC)−CN(TC))/CN(TC)=2.01; and the parameter connected with the zero-temperature thermodynamic critical field: R3=TCCN(TC)/HC2(0)=0.158. Finally, it has been shown that the value of the electronic effective mass is high: me⋆/me>2.

► High-pressure superconducting state in CaLi2.
► The Eliashberg formalism.
► Non-standard thermodynamic properties.