The correlation between the energy gap and the pseudogap temperature in cuprates: the YCBCZO and LSHCO case

The paper analyzes the influence of the hole density, the out-of-plane or in-plane disorder, and the isotopic oxygen mass on the zero temperature energy gap ($2\Delta\left(0\right)$) for $\rm{Y}_{1-x}\rm{Ca}_{x}\rm{Ba}_2\left(\rm{Cu}_{1-y}\rm{Zn}_{y}\right)_{3}\rm{O}_{7-\delta}$ (YCBCZO) and $\rm{La}_{1.96-x}\rm{Sr}_{x}\rm{Ho}_{0.04}\rm{CuO}_{4}$ (LSHCO) superconductors. It has been found that the energy gap is visibly correlated with the value of the pseudogap temperature ($T^{\star}$). On the other hand, no correlation between $2\Delta\left(0\right)$ and the critical temperature ($T_{C}$) has been found. The above results mean that the value of the dimensionless ratio $2\Delta\left(0\right)/k_{B}T_{C}$ can vary very strongly together with the chemical composition, while the parameter $2\Delta\left(0\right)/k_{B}T^{\star}$ does not change significantly. In the paper, the analytical formula which binds the zero temperature energy gap and the pseudogap temperature has been also presented.Comment: 7 pages, 4 figures, 3 table

Specifc Heat and Thermodynamic Critical Field for Calcium under the Pressure at 120 GPa

The free energy difference between the superconducting and normal state for Calcium under the pressure at 120 GPa has been determined. The numerical calculations have been made in the framework of the imaginary axis Eliashberg approach. On the basis of the obtained results the specific heat in the superconducting C^{S}(T) and normal C^{N}(T) state, as well as, the thermodynamic critical field H_{C}(T) have been obtained. It has been shown that the characteristic values of the considered thermodynamic quantities do not obey the BCS universal laws. In particular, {\Delta}C(T_{C})/C^N(T_{C})=2.48 and T_{C}C^{N}(T_{C})/H_{C}^{2}(0)=0.154.Comment: 3 pages, 4 figure

Strong-coupling description of the high-temperature superconductivity in the molecular hydrogen

The detailed study of the selected thermodynamic properties of the superconducting phase in the molecular hydrogen under the pressure at 428 GPa has been presented. For the increasing value of the Coulomb pseudopotential, $\mu^{*}\in$, the following results have been obtained: (i) the critical temperature decreases from 179 K to 141 K, (ii) the ratio $R_{1}\equiv\Delta(0)/k_{B}T_{C}$ differs noticeably from the BCS value: $R_{1}\in$; (iii) the electron effective mass is large and grows slightly together with the temperature ($[m^{*}_{e}/m_{e}]_{{\rm max}} = 2.2$ for $T = T_{C}$)