Influence of strong-coupling and retardation effects on superconducting state in $\mathrm{Y}{\mathrm{B}}_6$ compound

Abstract

In the framework of strong-coupling formalism, we have calculated the thermodynamic parameters of superconducting state in the $\mathrm{Y}{\mathrm{B}}_6$ compound. The values of critical temperature ($T_C$) are $9.5$~K and $7.9$~K for the Coulomb pseudopotential ${\mu }^{\star }=0.1$ and $0.2$, respectively. In the paper, we have determined the low temperature values of order parameter ($\Delta (0)$), specific heat jump at the critical temperature ($\Delta C(T_C)$), and thermodynamic critical field ($H_C(0)$). The dimensionless thermodynamic ratios: $R_{\Delta }=2\Delta \left(0\right)/k_B{T}_C$, $R_C=\Delta C\left(T_C\right)/C^N\left(T_C\right)$, and $R_H=T_C{C}^N\left(T_C\right)/H_C^2\left(0\right)$ are equal to: $R_{\Delta }\left({\mu }^{\star }\right)\in \{4.48,4.35\}$, $R_C\left({\mu }^{\star }\right)\in \{2.62,2.55\}$, and $R_H\left({\mu }^{\star }\right)\in \{0.146,0.157\}$. Due to the significant strong-coupling and retardation effects ($k_B{T}_C/{\omega }_{\ln }\sim 0.1$) those values highly deviate from the predictions of BCS theory.

5 pages, 4 figures