Influence of strong-coupling and retardation effects on superconducting state in ${\rm YB_{6}}$ compound

Abstract

In the framework of strong-coupling formalism, we have calculated the thermodynamic parameters of superconducting state in the ${\rm YB_{6}}$ 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: $R_{\Delta}=2\Delta\left(0\right)/{k_BT_C}$, $R_C=\Delta C\left(T_C\right)/C^N\left(T_C\right)$, and $R_H=T_CC^N\left(T_C\right)/H_C^2\left(0\right)$ are equal to: $R_{\Delta}\left(\mu^{\star}\right)\in\lbrace 4.48,4.35\rbrace$, $R_{C}\left(\mu^{\star}\right)\in\lbrace 2.62,2.55\rbrace$, and $R_{H}\left(\mu^{\star}\right)\in\lbrace 0.146,0.157\rbrace$. Due to the significant strong-coupling and retardation effects ($k_{B}T_{C} / \omega_{\rm ln}\sim 0.1$) those values highly deviate from the predictions of BCS theory.