Pressure weakens coupling strength in In and Sn elemental superconductors

Abstract

Pressure dependence of the thermodynamic critical field $B_{\mathrm{c}}$ in elemental indium (In) and tin (Sn) superconductors was studied by means of the muon-spin rotation/relaxation. Pressure enhances the deviation of $B_{\mathrm{c}}(T)$ from the parabolic behavior, expected for a typical type-I superconductor, suggesting a weakening of the coupling strengths $\alpha =⟨\Delta ⟩/k_{\mathrm{B}}{T}_{\mathrm{c}}$ ($⟨\Delta ⟩$ is the average value of the superconducting energy gap, $T_{\mathrm{c}}$ is the transition temperature and $k_{\mathrm{B}}$ is the Boltzmann constant). As pressure increases from 0.0 to $\simeq 3.0$ GPa $\alpha$ decreases linearly, by approaching the limiting weak-coupling BCS value ${\alpha }_{\mathrm{BCS}}=1.764$. Analysis of the data within the framework of the Eliashberg theory reveals that only part of the pressure effect on $\alpha$ can be attributed to the effect of hardening of the phonon spectra, which is reflected by a decrease of the electron-phonon coupling constant. Nearly 40% of the effect is caused by increased anisotropy of the superconducting energy gap.

6 pages, 3 figures

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Cited by in corpus (1)

• Thermodynamic evidence for a pressure-driven crossover from strong- to weak-coupling superconductivity in Pb