Cooper pair ring model

Abstract

The superconducting state starts to collapse when the externally applied magnetic field exceeds the Meissner-Ochsenfeld critical field, Bc,MO, which in type-I superconductors is the thermodynamic critical field, while in type-II superconductors this field is the lower critical field. Here we show that both critical fields can be described by the universal equation of $B$$_{c,MO}$=$\mu$$_0$$n$$\mu$$_B$$ln(1+2$$^{0.5}$$\kappa$), where $\mu$$_0$ is the magnetic permeability of free space, $n$ is the Cooper pairs density, and $\mu$$_B$ is the Bohr magneton, and $\kappa$ is the Ginzburg-Landau parameter. As a result, the Meissner-Ochsenfeld field can be defined as the field at which each Cooper pair exhibits the diamagnetic moment of one Bohr magneton with a multiplicative pre-factor of $ln(1+2$$^{0.5}$$\kappa$). In the two-dimensional case this implies that the Cooper pair center of mass is spatially confined within a ring with inner radius $\xi$ and outer radius of $\xi$+2$^{0.5}$$\lambda$, where $\xi$ is the coherence length and $\lambda$ is the London penetration depth. This means that the superconducting transition is associated not only with the charge carrier pairing, but that the pairs exhibit a new topological state with genus 1.