Surface superconductivity at high temperatures

Abstract

The possibility that surface superconductivity of the Ginzburg type might occur at high temperatures is investigated. The m ost likely effect is seen to be surface ordering brought about by resonance coupling through the impurity surface states. A m echanism is described by which the localized coherence which this requires can occur, giving transition temperatures orders of magnitudes higher than any now known.

Theory of the superconducting proximity effect

“…* In a clean system, K,o(r, r') reduces to the electron-hole pair propagator Go,(r, r')G _,o(r, r'), where G is the normalstate Green's function, while in dirty metals the kernel includes the effect of impurity scattering. It is assumed that the scattering is short range and isotropic, and that the distribution of scatterers is random and dilute, t 1 For a bulk superconductor the Fourier-transformed kernel is then 2rcN~ q 11-1 (9) Ko,(q) = hv~vF [_arctan ~o,q where N is the density of states at the Fermi surface, VF is the Fermi velocity, l is the electron mean free path, and (g 1 = l-1 + 21e)I/VF.…”

Impact of Correlated Disorder on Surface Superconductivity: Revealing the Robustness of the Surface Ordering Effect

“…Nearly six decades ago, the concept of “surface ordering” was introduced, which involves surface coupling between bulk quasiparticle states. , In the subsequent years, theoretical investigations of surface effects in conventional superconductors, in which the coherence length exceeds the Fermi wavelength, suggested that T c remains largely unaffected by boundaries. − However, recent theoretical predictions based on the tight-binding formulation of the Bogoliubov–de Gennes (BdG) equations have unveiled a marked increase in the superconducting critical temperature at surfaces . Surface superconductivity can persist well above the bulk critical temperature, attributed to surface-localized quantum constructive interference among BdG bulk eigenstates .…”

“…Because of the quantum phenomenon of constructive interference among distinct bulk eigenstates within the BdG system, an intriguing effect termed “surface ordering” emerges. ,,, Consequently, the presence of disorder, encompassing imperfections within the bulk, is anticipated to influence the critical temperature at the surface. To investigate the impact of disorder on the surface critical temperature, we employ a model incorporating bulk disorder, as described in eq .…”

Effect of Material-Dependent Boundaries on the Interference Induced Enhancement of the Surface Superconductivity Temperature

“…“ Surface ordering ” is based on the assumption that all quasiparticles on the surface contribute to the superconducting state. “Since most of these quasiparticles are in Bloch orbital states of real momentum, this means a near-surface localized correlation between orbits passing through the entire volume, rather than a correlation between quasiparticles in localized surface states.” In turn, “ surface ordering ” can already cause order in the bulk due to the proximity effect even at weaker interactions and, hence, modify the critical temperature near the surface.…”