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 (T-c = 12.9 K). 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: mu(star)(C) = 0.23. Generalizing the results, the function mu(star)(C) (p) has a high value (mu(star)(C) (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: R-1 equivalent to 2 Delta (0) /k(B)T(C) = 3.95; the ratio of the specific heat for superconducting (C-S) and the normal (C-N) state: R-2 equivalent to (C-S (T-C) - C-N (T-C)) / C-N (T-C) = 2.01; and the parameter connected with the zero-temperature thermodynamic critical field: R-3 = TCCN (T-C) /H-C(2) (0) = 0.158. Finally, it has been shown that the value of the electronic effective mass is high: m(e)(star)/m(e) > 2. (C) 2012 Elsevier Ltd. All rights reserved.