A classical model is presented for persistent currents in superconductors. Their existence is argued to be warranted because their decay would violate the second law of thermodynamics. This conclusion is achieved by analyzing comparatively Ohm's law and the Joule effect in normal metals and superconducting materials. Whereas Ohm's law applies in identical terms in both cases, the Joule effect is shown to cause the temperature of a superconducting sample to \textit{decrease}. An experiment is proposed to check the validity of this work in superconductors of both types I and II.
We propose a novel supercurrent generation mechanism in the cuprate. The supercurrent is generated as a collection of the spin-vortex-induced loop currents created with the doped holes at their centers. A quartet of the spin-vortices with width 4a (a is the lattice constant of the CuO 2 plane) is the stable unit of the spin-vortices, and an assembly of them create a network channel for the supercurrent flow. A macroscopic supercurrent flows when they cover the whole CuO 2 plane. The Ginzburg-Landau macroscopic wave function formalism is also derived from the present supercurrent generation mechanism.
It has been argued 1-3 recently that the Joule effect, induced as a by-product of the Meissner effect in superconductors, contradicts the BCS theory 4,5 . Conversely those publications 1-3 are shown below to run afoul at one another and to be at loggerheads with thermodynamics. Moreover, they turn out to be irrelevant to the BCS theory.
By taking advantage of a stability criterion established recently, the critical temperature Tc is reckoned with help of the microscopic parameters, characterising the normal and superconducting electrons, namely the independent-electron band structure and a repulsive two-electron force. The emphasis is laid on the sharp Tc dependence upon electron concentration and inter-electron coupling, which might offer a practical route toward higher Tc values and help to understand why high-Tc compounds exhibit such remarkable properties.
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