Channeled Vortex Motion: Fabrication of Vortex Channels

by Mr. Guy Bareli

Ben Gurion University

at Condensed Matter Seminar

Mon, 20 May 2019, 11:30
Sacta-Rashi Building for Physics (54), room 207

Abstract

Space-confined and controlled magnetic vortex motion in films of cuprate superconductors, such as YBa2Cu3O$7-\delta$ (YBCO, where $\delta$ denotes the level of oxygen doping), is an interesting ongoing research topic due to the potential involvement of coherent effects and appearance of quasi-Josephson effects. These mechanisms may offer an alternative to conventional Josephson devices, particularly in the case of cuprate superconductors that exhibit extremely short coherence lengths, thereby inspiring innovative designs for superconducting electronic devices. Space-controlled magnetic vortex motion state in a superconductor film can either occur spontaneously or be artificially induced by fabricated easy vortex motion channels. The spontaneous vortex motion phenomena are generally undesirable features because uncontrolled and random vortex dynamic usually result in noise and electronic instability.\r\nIn this research we focus on designing and perfecting new methods for fabricating these easy vortex motion channels, which offer new opportunities for further research of vortex dynamics in the coherent motion regime. The fabrication methods we design and investigate are laser writing (LW), electron writing (EW), and bi-layer channelling (BC). All method procedures are thoroughly described and then tested for their influence on superconductor material, superconductive characteristic variations induced by the different treatments, and technique optimization. Ultimately, the feasibility of creating easy vortex motion channels using all three proposed methods are examined and compared to one another.\r\nThe experimental phase of this research consisted of structural and transport measurements: structural experiments include micro-Raman spectroscopy and transmission electron microscopy, while transport measurements include resistance vs. temperature and voltage vs. current curves.\r\nResults show that the EW treatment offers a viable alternative to the more developed LW treatment with regard to fabricating vortex channels in thin-film YBCO superconductors, while using less complex machinery and procedures. Moreover, all methods tested exhibit the possibility of inducing coherent vortex motion and frequency lock state; in the BC case, however, this state was observed only for orientations of higher pinning magnitudes, when vortex motion was influenced by an effective periodic magnetic potential. Other orientations of the bi-layer did not exhibit coherent vortex motion for the entire range of external driving currents used in our experiments (𝐼 ≤ 120 𝑚𝐴), which might prove unsuitable for some superconductive devices, and one of the other proposed methods should be considered instead.\r\nKeywords: vortex motion, fabrication methods, vortex channelling, frequency lock.

Created on 13-05-2019 by Meidan, Dganit (dganit)
Updaded on 13-05-2019 by Meidan, Dganit (dganit)