Inhomogeneous superconducting states in two weakly linked superconducting ultra thin films

Kavli Affiliate: Yi Zhou

| First 5 Authors: Gao-Wei Qiu, Yi Zhou, , ,

| Summary:

A sufficiently large parallel magnetic field will generate staggered
supercurrent loops and superfluid density wave in two weakly linked
superconducting (SC) ultrathin films, resulting in an inhomogeneous
Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) state. The SC order parameter of such
an FFLO state is characterized by Bloch wave functions, called the "Bloch SC
state". The staggered supercurrent loops form an array of Josephson
vortex-antivortex pairs, instead of the usual Josephson vortex lattice.
Enclosing a unit cell of the array, the London’s fluxoid is quantized as
$Phi^{prime}=Phi_0=hc/2e$, while the net orbital magnetization caused by the
staggered supercurrent is zero. Meanwhile, a small parallel magnetic field
gives rise to an Fulde-Ferrell (FF) state that has uniform superfluid density.
The phase transition between the Bloch SC state and the FF state belongs to the
universality class of two-dimensional commensurate-incommensurate transitions.
An analytical solution in terms of Jacobian elliptic functions is found to be
an excellent approximation to the Bloch SC order parameter.

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