Microscopic description of surface superconductivity

Boundary conditions for the order parameter and the proximity influenced internal phase differences in double superconducting junctions

“…As distinct from the case χ = 0, both terms on the right-hand side of the boundary conditions (59) have negative sign at χ = π, as well as at all π/2 < |χ| ≤ π. For this reason, the sign of the order parameter derivative at χ = π is negative in the central electrode irrespective of the relation between f (l/2)−0 and f (l/2)+0 .…”

“…Possible reasons for the surface superconductivity enhancement have been considered in Refs. [58][59][60] and references therein. The depairing effects in the near-surface region can also be associated with an anisotropic pairing structure in unconventional superconductors [61][62][63][64][65][66][67][68][69][70][71].…”

“…As this follows from the boundary conditions (59) and the conservation of the supercurrent (60), the order parameter values f l/2±0 on opposite sides of an interface between identical superconductors can generally differ from one another. This is usually not the case in a single symmetric Josephson junction, where f (x) is continuous across a thin interface.…”

Interference-induced surface superconductivity: Enhancement by tuning the Debye energy

“…Let us consider a 1D chain of atoms with the s-wave pairing of electrons in the system and adopt the attractive Hubbard model within the tight-binding approximation. The related BdG equations can be written as [14][15][16][17][18]…”

“…However, recently it was found within the BdG equations for the Hubbard attractive model with the nearest-neighbor hopping that the relative difference between T cs and T cb can increase up to 20-25%, and this increase was attributed to the formation of boundary pair states with elevated critical temperatures [14]. Later it was shown [15,16] that in fact, the enlargement of the surface critical temperature is caused by the constructive interference of the bulk pair states near the sample surface. Such a constructive interference was found to be most pronounced when the conduction band is symmetric with respect to the Fermi level (the half-filling case).…”