Pressure Effect on the Einstein-Like Phonon Mode in Superconducting $\hbox {YB}_{6}$

Abstract

$\hbox {YB}_{6}$ is known as a conventional type-II BCS superconductor in which the strong coupling superconductivity with $2\Delta /k_{B}T_{c}\approx 4.1$ is mediated by the Einstein-like phonon mode of Y atoms located at $\hbar \omega _{E}\approx 8\,\hbox {meV}$. We have investigated the pressure effect on $\omega _{E}$ by Raman scattering up to 14 GPa. The received linear pressure increase in this mode $d\omega _{E}/dp\approx$ 0.21 meV/GPa yields an isothermal Grüneisen coefficient $\gamma _{T}= -\partial \hbox {ln}\omega _{E}/\partial \hbox {ln} V = 3.85$. Moreover, the pressure effect on the electron–phonon interaction $\lambda$ calculated from the McMillan–Allen–Dynes expression for the superconducting transition temperature was determined to be $\partial \hbox {ln}{\lambda }/\partial \hbox {ln}V \cong 7.2$.