Effect of diffusive boundaries on surface superconductivity in unconventional superconductors

Abstract

Boundary conditions for a superconducting order parameter at a di usive scattering boundary are derived from microscopic theory. The results indicate that for all but isotropic gap functions the di usive boundary almost completely suppresses surface superconductivity in the Ginzburg-Landau regime. This indicates that in anisotropic superconductors surface superconductivity can only be observed for surface normals along high symmetry directions where atomically clean surfaces can be cleaved. 74.60.Ec, 74.70.Tx Typeset using REVT E X

Surface superconductivity as the primary cause of broadening of superconducting transition in Nb films at high magnetic fields

“…Thus the full width of the transition is dominated by SSC. Although SSC is well known for carefully polished single crystals [7,9], it is usually considered to be insignificant for disordered, rough or inhomogeneous superconducting films because of its assumed fragility and sensitivity to surface conditions [1,6,8,10]. Therefore, observation of a very robust SSC in our strongly disordered polycrystalline films is rather surprising, especially for field perpendicular to the film.…”

“…1.69H c2 than bulk superconductivity [1], which can also smear the superconducting transition. Although SSC is quite profound in polished clean superconductors [6][7][8][9], it is usually ignored for disordered, polycrysstaline films because SSC is considered to be very sensitive to the quality of the surface (e.g., surface passivation [8] and order parameter suppression [1]), surface roughness [6,8] and surface scattering [10].…”

Onset of surface superconductivity beyond the Saint-James–de Gennes limit

“…The effect of anisotropy on H c3 was considered within GL theory [40]. The critical field was also analyzed for the case of unconventional pairing [41,42], and for the case of multiband superconductor in the context of MgB 2 assuming disordered dominated regimes that were treated with the help of semiclassical Usadel equations [43].…”

Observation of surface superconductivity and direct vortex imaging of a Pb thin island with a scanning tunneling microscope

“…From the linear Ginzburg-Landau (GL) equation for isotropic materials, a universal value 1.6946 for the ratio H c3 /H c2 can be obtained [2], which has stimulated extensive studies on the onset of superconductivity in higher fields in the past decades [3][4][5][6][7]. So far, the evidences of surface superconductivity had been shown only by transport measurements [3,4,7] and theoretical calculations [5,6]. Here, we report the real-space observation of the surface superconductivity by means of low-temperature high-magnetic-field scanning tunneling microscopy/spectroscopy (STM/STS).…”