Universal self-field critical current for thin-film superconductors

Abstract

For any practical superconductor the magnitude of the critical current density, $J_{\text{c}}$, is crucially important. It sets the upper limit for current in the conductor. Usually $J_{\text{c}}$ falls rapidly with increasing external magnetic field but even in zero external field the current flowing in the conductor generates a self-field which limits $J_{\text{c}}$. Here we show for thin films of thickness less than the London penetration depth, $\lambda$, this limiting $J_{\text{c}}$ adopts a universal value for all superconductors - metals, oxides, cuprates, pnictides, borocarbides and heavy Fermions. For type I superconductors, it is $H_{\text{c}}/\lambda$ where $H_{\text{c}}$ is the thermodynamic critical field. But surprisingly for type II superconductors we find the self-field $J_{\text{c}}$ is $H_{\text{c}1}/\lambda$ where $H_{\text{c}1}$ is the lower critical field. $J_{\text{c}}$ is thus fundamentally determined and this provides a simple means to extract absolute values of $\lambda (T)$ and, from its temperature dependence, the symmetry and magnitude of the superconducting gap.

8 pages, 6 figures

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• Condensate flow in holographic models in the presence of dark matter
• The electron-phonon coupling constant, the Fermi temperature and unconventional superconductivity in the carbonaceous sulfur hydride 190 K superconductor
• Peak in the critical current density in (Ca${}_x$Sr${}_{1-x}$)${}_3$Rh${}_4$Sn${}_{13}$ tuned towards the structural quantum critical point
• Method to extracting the penetration field in superconductors from DC magnetization data
• High $J_{\mathrm{c}}$ and low anisotropy of hydrogen doped NdFeAsO superconducting thin film