Anomalous gap ratio in anisotropic superconductors: Aluminum under pressure

Abstract

Pressure dependence of the thermodynamic critical field Bc in elemental aluminum was studied by means of the muon-spin rotation-relaxation technique. Pressure enhances the deviation of Bc(T) from parabolic behavior, expected for a typical type-I superconductor, thus suggesting the weakening of the gap ratio 〈α〉=〈Δ〉/kBTc (〈Δ〉 is the average value of the superconducting energy gap, Tc is the transition temperature, and kB is the Boltzmann constant). With the pressure increase from 0.0 to ≃1.6 GPa, 〈α〉 decreases almost linearly from 1.73(1) to 1.67(1). Our results imply, therefore, that in elemental aluminum, the gap ratio 〈α〉 is smaller than the weak-coupled BCS prediction αBCS≃1.764, and it is even further reduced under pressure.

Source-reported materials — not catalogue approval

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