The 0.3-mm-thick, 50-mm-wide and 100-mm-long YBa2Cu3O7-x superconducting bridges with a laser-written, single, Π-shaped channel have been investigated by means of electronic transport measurements at temperatures below the onset of the bridge's superconducting transition temperature. Our results demonstrate that the coherent vortex motion confined in the P-shaped channel can be used for determination of both the density and velocity of Abrikosov magnetic vortices in the channel. The coherent motion of Abrikosov vortices expresses itself as Josephson-like voltage steps, observed on the current-voltage characteristics of our microbridges, measured at zero external magnetic field, in a limited range of temperatures and bias currents. The steps' amplitude corresponds to the entrance of an additional vortex-antivortex pair into the channel's area and change in the vortex velocity. This amplitude also affects the increase of the Lorentz force for energy dissipative drift of the magnetic flux in the channel, but it does not increase, however, with the increase of the biasing current. We present and discuss the results of experimentally measured and calculated energy dissipation, which originated from variations in the vortex density and velocity when the vortices are moving along the channel of the superconducting bridge.http://dx.doi.org/10.5755/j01.ms.17.2.489

A current-self-induced magnetic field Hj, such that Hc1 < Hj < Hc2 at T < Tc, penetrates a thin-film, type-II superconductor forming the Abrikosov magnetic vortex-antivortex pairs in the film's areas of weakest superconductivity. Our atomic force microscopy and scanning tunneling microscopy images confirm that in 50 µm wide, 100 µm long and 0.3 µm thick YBa2Cu3O7−x superconducting devices magnetic flux penetrates first into a 5 µm wide, Π-shaped and partially deoxygenated (x ≈ 0.2) channel for easy vortex motion. When the Lorentz force overcomes pinning force in the channel, the flux starts to move and its drift dissipates energy inducing dc voltage. This work reports on the density of coherently moving vortices along the channel vs. temperature in range from 0.93Tc to 0.97Tc. Our simulations show that the vortex density vs. temperature dependence extracted from I-V measurements of our devices follows the temperature dependence of magnetic field penetration depth and the coherence length of the superconductor.

A mixed state in dc-biased thin films of II-type superconductors realizes the Abrikosov magnetic vortices/ antivortices, which are the result of the current-self magnetic field penetration into the film at temperatures lower than its critical temperature Tc. A nucleation of vortices/antivortices at the superconducting film's edges, their motion perpendicular to the direction of biasing current, and the annihilation in the film's center originates from a current dissipation in the superconductor and expresses itself in experiments as a dc voltage. This work reports on the results of simulation of current density in a 50 µm wide, 100 µm long, and 0.3 µm thick YBa2Cu3O7−x microbridges containing Π-shaped 5 µm wide single channel of easy vortex motion fabricated by means of laser-writing technique. Analyzing a two-dimensional-net of resistors and assuming that, due to the Meissner-Ochsenfeld effect, the magnetic flux penetration into superconducting film is nonlinear, we demonstrate that presence of a Π-shaped channel causes a non-homogeneous distribution of current in the microbridge.

Results of our research demonstrate possibilities of detection of microwaves radiation by means of asymmetrically narrowed YBa 2 Cu 3 O 7-x oxygen-rich (x ≤ 0.2) and oxygen-decomposed (x > 0.5) in the necked region at temperatures higher than the critical temperature of the superconductor T c at which superconductor exhibits properties of a heavilydoped semiconductor. Both types of structures, mounted into a 10 GHz waveguide, generate sub-linearly increasing amplitude of detected voltage with increase of incident power of pulsed 10-GHz-frequency microwave radiation. The voltage sensitivity S x ≤ 0.2 ≥ 1.3 mV/W of oxygen-rich and S x > 0.5 ≥ 9 mV/W of oxygen-decomposed structure were measured at room temperature. Asymmetrical shape of nonlinear current-voltage dependences depend on oxygen content x in the necked region and temperature of the tested structure. Our results show that the asymmetrically narrowed structure with a necked region down to 10 μm made of partially deoxygenated YBa 2 Cu 3 O 7-x superconductor can be used as a nonsuperconducting, nonlinear on-chip element (detector of MW power) in the YBa 2 Cu 3 O 7-x chip operating at temperatures below critical temperature T c of the chip superconductor.

StiprioS I >> I c elektros srovės tankio pasiskirstymas plonuose y-Ba-Cu-o sluoksniuose, turinčiuose silpnojo superlaidumo sritis jonas Šulcas 1 , artūras jukna 2 Vilniaus Gedimino technikos universitetas El. paštas: 1 j.sulcas@etronika.lt; 2 arturas.jukna@vgtu.lt santrauka. Nagrinėjamas elektros srovės pasiskirstymas YBa 2 Cu 3 O 7-x superlaidininko plonuose sluoksniuose, kuriuose lazerio spinduliu suformuoti Π formos sūkurių kanalai. Superlaidžiajame darinyje atsiradus sūkurių kanalui, srovės tankis lokaliose darinio vietose gali skirtis 5 ir daugiau kartų, priklausomai nuo kanalo geometrijos. Darbe eksperimentiškai nustatyta, kad Abrikosovo magnetinių sūkurių koherentinis judėjimas sūkurių kanale siaurame temperatūrų ruože nuo 85,1 K iki 90,2 K prasideda superlaidžiuoju dariniu tekant I ~ I c ir išlieka iki ypač stiprių srovių I > 200I 1st step . Čia I 1st step -srovės stipris, kuriam esant sūkurių kanale vyksta koherentinis sūkurių judėjimas, o I c -kritinė superlaidininko srovė. Koherentinis sūkurių judėjimas kanalo srityje eksperimentuose pasireiškia darinių voltamperinėse charakteristikose elektros įtampos "laipteliais", kurių aukštis beveik nepriklauso nuo dariniu tekančios srovės stiprio. Eksperimentiniai rezultatai paaiškinti koherentinio sūkurių judėjimo ypatumais Π formos sūkurių kanalu.