Pressure effect on the superconducting and the normal state of β−Bi2Pd

Abstract

The pressure effect up to 24.0 kbar on superconducting and normal-state properties of $\ensuremath{\beta}\ensuremath{-}\mathrm{B}{\mathrm{i}}_{2}\mathrm{Pd}$ single crystal (${T}_{\mathrm{c}}\ensuremath{\approx}4.98\phantom{\rule{0.16em}{0ex}}\mathrm{K}$ at ambient pressure) has been investigated by measurements of the electrical resistivity. In addition, we have performed the heat capacity measurements in the temperature range 0.7--300 K at ambient pressure. The recent calculations of electronic density of states, electron-phonon interaction spectral function, and phonon density of states of $\ensuremath{\beta}\ensuremath{-}\mathrm{B}{\mathrm{i}}_{2}\mathrm{Pd}$ [Zheng and Margine, Phys. Rev. B 95, 014512 (2017)], are used to fit the resistivity and the heat capacity data. In the superconducting state we have focused on the influence of pressure on the superconducting transition temperature ${T}_{\mathrm{c}}$ and upper critical field ${H}_{\mathrm{c}2}$ and a negative effect with $d{T}_{\mathrm{c}}/dp=--0.025\phantom{\rule{0.16em}{0ex}}\mathrm{K}/\mathrm{kbar}$ and $d{H}_{\mathrm{c}2}/dp=--8\phantom{\rule{0.16em}{0ex}}\mathrm{mT}/\mathrm{kbar}$ is found. A simplified Bloch-Gr\uneisen model was used to analyze the pressure effect on the temperature dependence of the normal-state resistivity. The obtained results point to a decrease of the electron-phonon coupling parameter \ensuremath{\lambda} and to a shift of phonon frequencies to higher values with pressure. Moreover, the temperature dependence of the normal-state resistivity follows a ${T}^{2}$ dependence above ${T}_{\mathrm{c}}$ up to about 25 K. Together with the enhanced value of Sommerfeld coefficient $\ensuremath{\gamma}=13.23\phantom{\rule{0.16em}{0ex}}\mathrm{mJ}\phantom{\rule{0.16em}{0ex}}\mathrm{mo}{\mathrm{l}}^{\ensuremath{-}1}\phantom{\rule{0.16em}{0ex}}{\mathrm{K}}^{\ensuremath{-}2}$ these results point to a certain role of the electron-electron interaction in the superconducting pairing mechanism in $\ensuremath{\beta}\ensuremath{-}\mathrm{B}{\mathrm{i}}_{2}\mathrm{Pd}$.