Laser scanning microscopy of guided vortex flow in microstructured high-Tc films

Abstract

We report the visualization of guidance of vortices by artificial microholes ͑antidots͒ in superconducting thin films using a low-temperature laser scanning microscope. Previously, guided motion of vortices via tilted rows of antidots in YBa 2 Cu 3 O 7 films was detected indirectly by using resistive Hall-type measurements. Here we prove that vortices are steered between antidots into a priori chosen direction by imaging of resistive photoresponse with a spatial resolution down to about 1 m. We observe predominant paths for vortex motion. Vortices are nucleated and annihilated at antidots, i.e., antidots define starting and ending points of predominant vortex paths. Depending on the misorientation angle between rows of antidots and the current-driven direction of vortex motion, different channels dominate in antidot-guided vortex motion. Our experimental results can be explained by the n-channel model. Finally, we present direct measurements of the local critical currents. This technique can be used as a quantitative method for the analysis of vortex motion in micropatterned thin films.

Imaging of vortex flow in microstructured high-Tc films by laser scanning microscope

“…This difference in I c is higher than that one we measured on the same sample covered by gold (Ref. [8]). The holes occupy some place and reduce a cross-section of the sample within the rows, decreasing there the critical current.…”

“…Here we present the new results obtained using the previously measured samples [8]. This time we significantly improved the contrast and spatial resolution of the method by removing a thin Au layer, which covered high-T c film in the previous experiments [8].…”

“…[8], the LSM method allows us to directly measure exact values for local critical currents and, in a certain sense, a local I-V curves of any point of the sample. In this case, instead of scanning the whole surface, we focus the laser beam at some chosen position on the sample and measure the local voltage response dV as a function of the total bias current I b through the sample.…”

“…This time we significantly improved the contrast and spatial resolution of the method by removing a thin Au layer, which covered high-T c film in the previous experiments [8]. Removal of the gold layer enabled measurement of a spatial distribution of the local critical currents with a much higher accuracy.…”

Domain-wall and reverse-domain superconducting states of a Pb thin-film bridge on a ferromagnetic BaFe12O19single crystal

“…20,21 Here we report on the direct imaging of the development of DWS and RDS in a hybrid S/F PHYSICAL REVIEW B 84, 020505(R) (2011) structure, consisting of a superconducting Pb film on top of a ferromagnetic BFO crystal by means of LTSLM. 18,[22][23][24][25] We prepared a 40-nm-thick and 30-μm-wide Pb microbridge on top of a BFO substrate, so that only a single domain wall is running along the center of the Pb bridge parallel to the current flow. The BFO substrate and the Pb thin film were separated by a 4-nm-thick insulating Ge layer so that the system is only flux coupled.…”