Crossover between different regimes of inhomogeneous superconductivity in planar superconductor-ferromagnet hybrids

Abstract

11 pages, 12 figuresInternational audienceWe studied experimentally the effect of a stripe-like domain structure in a ferromagnetic BaFe_{12}O_{19} substrate on the magnetoresistance of a superconducting Pb microbridge. The system was designed in such a way that the bridge is oriented perpendicular to the domain walls. It is demonstrated that depending on the ratio between the amplitude of the nonuniform magnetic field B_0, induced by the ferromagnet, and the upper critical field H_{c2} of the superconducting material, the regions of the reverse-domain superconductivity in the H-T plane can be isolated or can overlap (H is the external magnetic field, T is temperature). The latter case corresponds to the condition B_0/H_{c2}<1 and results in the formation of superconductivity above the magnetic domains of both polarities. We discovered the regime of edge-assisted reverse-domain superconductivity, corresponding to localized superconductivity near the edges of the bridge above the compensated magnetic domains. Direct verification of the formation of inhomogeneous superconducting states and external-field-controlled switching between normal state and inhomogeneous superconductivity were obtained by low-temperature scanning laser microscopy

The diode effect induced by domain-wall superconductivity

“…, the magnetic flux quantum 0 = π hc/e and the superconducting bulk critical temperature T c0 in zero magnetic field. Therefore, for the step-like field distribution the developed DWS can be formed only if |H | B 0 and provided that H c2 < B 0 < H c3 (see, e.g., [12]). For the 0953-8984/14/095702+07$33.00 field patterns with a finite width of the transient area near the line b z (x, y) = 0 (i.e., a finite width of the DW) the criterion for DWS formation has to be dependent on the DW width [8].…”

Electric readout of magnetic stripes in insulators

“…Anisotropic transport phenomenon in superconductors induced by fixed nanofabricated artificial grooves 11 , magnetic lines 12 , or so-called domain wall superocnductivity was reported in ferromagnet/superconductor hybrids 17–19 . In the nanostructured grooves and magnetic lines, they act as fixed guidance of vortices, different from our study that demonstrates writing and reading operations from rewritable and tunable magnetic stripes in insulator films.…”

Edge superconductivity in Nb thin film microbridges revealed by integral and spatially resolved electric transport

“…To visualize the current distribution for different bias points in the T − H phase diagram, we used LTSLM. [38][39][40][41] For imaging by LTSLM, the sample was mounted on a cold finger of a Helium flow cryostat, which is equipped with an optical window to enable irradiation of the sample in the (x, y) plane by a focused laser beam with beam spot diameter ∼ 1.5−2 µm. 39,40 The amplitude modulated laser beam (at frequency f ≈ 10 kHz) induces a local increase of temperature centered at the beam spot position (x 0 , y 0 ) in the sample.…”