Anomalous gap ratio in anisotropic superconductors: aluminum under pressure

Abstract

Pressure dependence of the thermodynamic critical field $B_{\mathrm{c}}$ in elemental aluminum was studied by means of the muon-spin rotation/relaxation technique. Pressure enhances the deviation of $B_{\mathrm{c}}(T)$ from the parabolic behavior, expected for a typical type-I superconductor, thus suggesting the weakening of the gap ratio $⟨\alpha ⟩=⟨\Delta ⟩/k_{\mathrm{B}}{T}_{\mathrm{c}}$ ($⟨\Delta ⟩$ is the average value of the superconducting energy gap, $T_{\mathrm{c}}$ is the transition temperature and $k_{\mathrm{B}}$ is the Boltzmann constant). With the pressure increase from 0.0 to $\simeq 1.6$ GPa, $⟨\alpha ⟩$ decreases almost linearly from 1.73 to 1.67. Our results imply, therefore, that in elemental aluminum the gap ratio $⟨\alpha ⟩$ is smaller than the weak-coupled BCS prediction ${\alpha }_{\mathrm{BCS}}\simeq 1.764$ and it is even further reduced under pressure.

arXiv comment6 pages, 3 figures

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Cited by in corpus (6)

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• Anomalously small superconducting gap in the strong spin-orbit coupled superconductor: $\beta -$Tungsten
• Optical setup for a piston-cylinder type pressure cell: a double-volume approach