Interplay of flux guiding and Hall effect in Nb films with nanogrooves

Abstract

The interplay between vortex guiding and the Hall effect in superconducting Nb films with periodically arranged nanogrooves is studied via four-probe measurements in standard and Hall configurations and accompanying theoretical modeling. The nanogrooves are milled by focused ion beam and induce a symmetric pinning potential of the washboard type. The resistivity tensor of the films is determined in the limit of small current densities at temperatures close to the critical temperature for the fundamental matching configuration of the vortex lattice with respect to the pinning nanolandscape. The angle between the current direction with respect to the grooves is set at seven fixed values between $0^\circ$ and $90^\circ$. A sign change is observed in the temperature dependence of the Hall resistivity $\rho_\perp^-$ of as-grown films in a narrow temperature range near $T_c$. By contrast, for all nanopatterned films $\rho_\perp^-$ is nonzero in a broader temperature range below $T_c$, allowing us to discriminate between two contributions in $\rho_\perp^-$, namely one contribution originating from the guided vortex motion and the other one caused by the Hall anomaly just as in as-grown Nb films. All four measured resistivity components are successfully fitted to analytical expressions derived within the framework of a stochastic model of competing isotropic and anisotropic pinning. This provides evidence of the model validity for the description of the resistive response of superconductor thin films with washboard pinning nanolandscapes.