Critical behavior of layered superconducting films in a parallel magnetic field

Abstract

The equilibrium magnetization for layered superconducting films that experience a nonzero component H ʈ of magnetic field applied parallel to the layers is computed at temperatures and at perpendicular field components in the vicinity of the decoupling transition. A fermion analogy is exploited for this purpose, whereby it is found that the parallel magnetization shows an anomalous H ʈ Ϫ1 tail at high fields due to entropic fluctuations of the ͑parallel͒ lattice of Josephson vortices. A collective pinning effect is also identified for c-axis transport limited by a single planar defect oriented parallel to both c and to the applied magnetic field.

Theory of decoupling in the mixed phase of extremely type-II layered superconductors

“…(The logarithmically divergent contribution above that is equal to L At arbitrary number of layers and at arbitrary temperatures, the fermion analogy can be treated in the mean-field approximation defined by the charge-density wave (CDW) order parameter χ l (x) = Ψ † R (x, l)Ψ L (x, l) and the associated gap equation 42 ∆ l = U χ l + U ⊥ (χ l+1 + χ l−1 ). Standard self-consistent calculation yields a single-particle gap…”

“…The above renormalized LD model is known to be macroscopically Josephson coupled at temperatures below k B T * 0 = 4π J . [21][22][23][24]41,42 To illustrate this fact, consider first the minimal double-layer case, N = 2. The zero-temperature line tension of a single Josephson vortex is equal to the linear energy density…”

“…At the unbinding temperature k B T LE = 2π J for Josephson vortex/anti-vortex pairs, 41,42 on the other hand, the double-layer LD model can be analyzed exactly through a mapping to ideal spinless fermions (see Appendix B). The line-tension so obtained is given by the expression…”

Superconductivity versus tunneling in a doped antiferromagnetic ladder

“…On the basis of this mean-field analysis, 17 we conclude that the present ladder model allows no coherent transport whatsoever in between chains in the (rung) hole-pair regime.…”

“…11 We presume, therefore, that spin excitations are frozen out due to a relatively large spin gap of order ∆ spin ∼ J/2. A bosonization analysis based on the corresponding Luther-Emery model, 12−15 and generalizations thereof, 16,17 yields that the appearance of hole pairs along rungs coincides with the absence of coherent tunneling in between chains, as well as with the creation of a gap for single-particle excitations along chains. Also, while the hole pairs generally crystallize into a charge density-wave (CDW) state in the weak-coupling limit, 3 we predict that they Bose condense into an IPT-type superconductor at large enough binding energies (see Fig.…”