ИСТИНА

Local laser heating is a powerful tool to manipulate single vortices in superconducting films with high intrinsic pinning. Single vortices can be moved by tightly focused laser beam creating the temperature gradient, which exceeds a critical threshold for depinning, and can induce reversible displacement of the vortex cluster or single vortex. Reversible shifts of single vortex may be useful for the creation of new types of fluxtronic devices: optically governed RSFQ logics and so on. Comparing with MFM tip manipulation [1] this technique has a much larger scale of operation, higher operation frequencies and possibility to work with strong pinning samples. When the thermal force acting on the vortex which is proportional to the temperature gradient exceeds the local pinning force (Fp ~ϕ0Jc(T)d, d is the film thickness) single vortex can be shifted from one pinning center to another. The critical temperature gradient to unpin trapped vortices is proportional to the critical current density Jc(T) [2]. Improved magneto-optical technique capable of single vortex resolution [3] was applied for imaging of vortex motion under the influence of thermal gradient produced by the focused laser beam λ=532nm, 560nm and 633nm. Single molecule spectroscopy [4] was used to probe the temperature distribution around the hot spot by monitoring the linewidth broadening in fluorescence excitation spectra for single molecules distributed near the center of the focused laser beam with different local temperatures. With known temperature distribution near the hot spot the local pinning force distribution in Nb film with the thickness of 450 nm within area of view ~100x100 μm2 was found. For different initial flux density the radius of the thermally depinned area associated with the critical temperature gradient, and its dependence on the power of the laser beam P, initial temperature Tin, laser spot diameter r0 was measured. We compared the data on the critical current density Jc(T) found from experiments on thermal depinning with local heating by the focused laser beam with Jc(T) obtained from transport measurements.