Electron-phonon coupling and pairing mechanism in β−Bi2Pd centrosymmetric superconductor

Abstract

We report first-principles calculations of the superconducting properties of β-Bi2Pd within the fully anisotropic Migdal-Eliashberg formalism. We find a single anisotropic superconducting gap of s-wave symmetry which varies in magnitude on the different regions of the Fermi surface. The calculated superconducting energy gap on the Fermi surface, the superconducting transition temperature, the specific heat, and the quasi-particle density of states are in good agreement with the corresponding experimental results and support the view that β-Bi2Pd is a phonon-mediated single anisotropic gap superconductor.

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

“…III C. In the last paragraph of Sec. III D we present experimental data of the heat capacity at ambient pressure, which we compare with the calculations based on the theoretically predicted phonon density of states (PHDOS) [9]. The obtained Sommerfeld coefficient is significantly smaller than that from experiment.…”

“…Using isotropic Eliashberg spectral function α 2 F (ω) from Ref. [9], we can calculate the temperature dependence of the resistivity via formula:…”

“…We have checked that there is no significant difference in results taking α 2 F (ω) from Ref. [9] with or without spin-orbit coupling (SOC). For the sake of simplicity, we will thus in the following refer only to α 2 F (ω) calculated with SOC included.…”

“…Especially, in case of superconducting materials, the study of pressure influence on superconducting parameters can shed light on coupling mechanism of Cooper pairs [1,2]. Recently, the compound β-Bi 2 Pd has attracted interest due to controversial results about the origin of superconductivity, where there are some indications on a multigap superconductivity [3], topologically protected surface states [4,5,6], as well as a standard conventional superconductivity in this system [7,8,9]. Therefore, we decided to study the influence of high pressure on superconducting parameters of β-Bi 2 Pd, and perform additional measurements of its normal-state properties.…”

“…III B we present resistivity measurements in the normal state between 5 and 300 K and up to 24.0 kbar. The resistivity data at ambient pressure can be fitted by the Bloch-Grüneisen formula based on the theoretically predicted electron-phonon interaction spectral function α 2 F (ω) [9], but also by its simplified version with a single-phonon mode. The latter model applied on the normal-state resistivity at increasing pressure provides evidence that the dominant phonon frequency is shifted higher and the electron-phonon coupling constant is decreasing upon increasing pressure causing a lower T c .…”