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The resistance R versus perpendicular external magnetic field H was measured for superconducting Nb thin film microbridges with and without microholes (antidots, ADs). Well below the transition temperature, integral R.H/ measurements of the resistive transition to the normal state on the plain bridge show two distinct regions, which can be identified as bulk and edge superconductivity, respectively. The latter case appears when bulk superconductivity becomes suppressed at the upper critical field Hc2 and below the critical field of edge superconductivity Hc3 = 1.7Hc2. The presence of additional edges in the AD bridge leads to a different shape of the R.H/ curves. We used low-temperature scanning laser microscopy (LTSLM) to visualize the current distribution in the plain and AD bridges upon sweeping H. While the plain bridge shows a dominant LTSLM signal at its edges for H ≥ Hc2 the AD bridge also gives a signal from the inner parts of the bridge due to the additional edge states around the ADs. LTSLM reveals an asymmetry in the current distribution between the left and right edges, which confirms theoretical predictions. Furthermore, the experimental results are in good agreement with our numerical simulations (based on the time-dependent Ginzburg-Landau model), yielding the spatial distribution of the order parameter and current density for different bias currents and H values. [ABSTRACT FROM AUTHOR]

The experimental investigation of the Ic.B/-Tc.B/ phase boundary of superconducting niobium films with large area quasihexagonal hole arrays is reported. The hole arrays were patterned with microsphere photolithography. We investigate the perforated niobium films by means of electrical directed current transport measurements close to the transition temperature Tc in perpendicularly applied magnetic fields. We find pronounced modulations of the critical current with applied magnetic field, which we interpret as a consequence of commensurable states between the Abrikosov vortex lattice and the quasihexagonal pinning array. Furthermore, we observe Little-Parks oscillations in the critical temperature versus magnetic field. [ABSTRACT FROM AUTHOR]

We investigate the nucleation of superconductivity in a superconducting Al strip under the influence of the magnetic field generated by a current-carrying Nb wire, perpendicularly oriented and located underneath the strip. The inhomogeneous magnetic field, induced by the Nb wire, produces a spatial modulation of the critical temperature Tc, leading to a controllable localization of the superconducting order parameter (OP) wavefunction. We demonstrate that close to the phase boundary Tc.Bext/ the localized OP solution can be displaced reversibly by either applying an external perpendicular magnetic field Bext or by changing the amplitude of the inhomogeneous field. [ABSTRACT FROM AUTHOR]

We experimentally investigate the magnetic field dependence of the critical current Ic(B) of superconducting niobium thin films patterned with periodic and quasiperiodic antidot arrays on the submicron scale. For this purpose we monitor current–voltage characteristics at different values of B and temperature T. We investigate samples with antidots positioned at the vertices of two different tilings with quasiperiodic symmetry, namely the Shield Tiling and the Tuebingen Triangle Tiling. For reference we investigate a sample with a triangular antidot lattice. We find modulations of the critical current for both quasiperiodic tilings, which have partly been predicted by numerical simulations but not observed in experiments yet. The particularity of these commensurability effects is that they correspond to magnetic field values slightly above an integer multiple of the matching field. The observed matching effects can be explained by the caging of interstitial vortices in quasiperiodically distributed cages and the formation of symmetry-induced giant vortices. [ABSTRACT FROM AUTHOR]