Coherent magnetic vortex motion in optically formed channels for easy flow in YBa_2Cu_3O_(7-x) superconducting thin films

摘要

We report our results of investigation of electric and magnetic properties of partially oxygen-depleted channels for easy vortex motion in YBa_2Cu_3O_(7-x) (YBCO) superconducting, 50-μm-wide, and 100-μm-long micro-bridges at temperatures below the onset of the superconducting state critical temperature 7_c~(on). The channels were produced by means of a laser-writing technique. The writing was performed using a 0.1-0.3 W power, continuous-wave laser radiation focused down to a ～ 5 urn spot on the surface of a superconducting film in a nitrogen gas atmosphere, and resulted in perpendicular stripes (channels) with partial (x ～ 0.2) reduction of the oxygen content in the YBCO stripe. The oxygen-depleted channels exhibit a depressed T_c and lower both the critical current density and the first critical magnetic field, as compared with the laser-untreated areas. The bias current applied to the bridge self-produced a magnetic flux that penetrated the channels in a form of Abrikosov magnetic vortices that, subsequently, moved coherently (a quasi-Josephson effect) along the channels in the narrow temperature range of 0.943 T_c~(on)-0.98 T_c~(on) and manifested themselves as steps on the current-voltage characteristics of our microbridges. Our results demonstrate that laser-induced formation of artificial channels of the flux flow can be used for a precise control of vortex nucleation and their coherent motion in pre-assigned regions of thin-film YBCO devices.