Abstract
For any practical superconductor the magnitude of the critical current density, Jc, is crucially important. It sets the upper limit for current in the conductor. Usually Jc falls rapidly with increasing external magnetic field, but even in zero external field the current flowing in the conductor generates a self-field that limits Jc. Here we show for thin films of thickness less than the London penetration depth, λ, this limiting Jc adopts a universal value for all superconductors—metals, oxides, cuprates, pnictides, borocarbides and heavy Fermions. For type-I superconductors, it is Hc/λ where Hc is the thermodynamic critical field. But surprisingly for type-II superconductors, we find the self-field Jc is Hc1/λ where Hc1 is the lower critical field. Jc is thus fundamentally determined and this provides a simple means to extract absolute values of λ(T) and, from its temperature dependence, the symmetry and magnitude of the superconducting gap.
Highlights
The vortices mutually annihilate at the centre and the process continues indefinitely causing dissipation. This vortex entry from the faces defines a first critical current density given by the equality sign in equation (8), which is alternative to a second, which is associated with vortex entry from the edges
We have shown that for thin films of thickness bol, the self-field Jc is given by Hc/l for type-I superconductors and Hc1/l for typeII superconductors
We predict a second peak in Jc(p, sf) near pE0.12, near which charge ordering occurs[33], and we suggest that, for Zn-substituted YBa2Cu3Oy, Jc(sf)2/3 will be suppressed by impurity scattering in the same canonical manner as the superfluid density
Summary
For each of these samples, the fit to the weak-coupling d-wave model is excellent across the entire temperature range. This is surprising because other techniques such as muon spin relaxation[8] suggest that the T-dependence of rs does not always follow the canonical d-wave form. Cichorek et al.[9] determined Jc(T) from remanent magnetization measurements This is shown by the magenta symbols and, significantly, Jc(T) shows an enhancement below 0.65 K that almost exactly mirrors our Jc(T) values calculated from Hc1. In each case the correlation is excellent and it is this that validates our primary conclusion
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