Thermodynamic Parameters of Single‐ or Multi‐Band Superconductors Derived from Self‐Field Critical Currents

Abstract

Key questions for any superconductor include: what is its maximum dissipation-free electrical current (its 'critical current') and can this be used to extract fundamental thermodynamic parameters? Present models focus on depinning of magnetic vortices and implicate materials engineering to maximise pinning performance. But recently we showed that the self-field critical current for thin films is a universal property, independent of microstructure, controlled only by the penetration depth. Here we generalise this observation to include thin films, wires or nanowires of singleor multi-band s-wave and d-wave superconductors. Using extended BCS equations we consider dissipation-free self-field transport currents as London-Meissner currents, avoiding the concept of pinning altogether. We find quite generally, for type I or type II superconductors, the current is limited by the relevant critical field divided by the penetration depth. Our fits to 64 available data sets, from zinc nanowires to compressed sulphur hydride with critical temperatures of 0.65 to 203 K, respectively, are excellent. Extracted London penetration depths, superconducting energy gaps and specific heat jumps agree well with reported bulk values. For multiband or multiphase samples we accurately recover individual band contributions and phase fractions.

Classifying hydrogen-rich superconductors

“…In our recent paper [14], we deduced (0) in H3S more accurately in comparison with values we used to calculate , ℎ and , in our previous papers [57,62]. By taking in account that H3S exhibits  = 88-105 [57,62,65], we revisited , ℎ and , at two applied pressures of P = 155 GPa and 160 GPa (Table III) To calculate , ℎ and , (Eqs. 36,37) for compressed LaH10 there is a need to make an assumption about the value for Ginzburg-Landau parameter, .…”

Unconventional superconductivity in highly-compressed unannealed sulphur hydride

“…From deduced (0) values ( Fig. 1 and Table 1), we calculated the Fermi temperature, TF, For H3S phase  = 3.53-4.7, where the lower bound was reported by Kaplan and Imry [34] and in our previous works [35][36][37], and the upper bond was reported by other authors [3,32]. Due to for all three models deduced Tc = 45.9 ± 0.1 K in Table I we show only the Tc/TF ratios.…”

Classifying superconductivity in Moiré graphene superlattices

“…In Eq. 9 the value of  = 7/5 [58]. The fit to this model does not converge, as the value m(0) tends toward an infinitely large value.…”

“…where m(T) is the is the maximum amplitude of the k-dependent d-wave gap given by Eq. 9,  is the angle around the Fermi surface subtended at (, ) in the Brillouin zone (details can be found elsewhere [58,59]). In Eq.…”