Direct Visualization of Current-Stimulated Oxygen Migration in YBa2Cu3O7−δ Thin Films

The past years have witnessed major advancements in all-electrical doping control on cuprates. In the vast majority of cases, the tuning of charge carrier density has been achieved via electric field effect by means of either a ferroelectric polarization or using a dielectric or electrolyte gating. Unfortunately, these approaches are constrained to rather thin superconducting layers and require large electric fields in order to ensure sizable carrier modulations. In this work, we focus on the investigation of oxygen doping in an extended region through current-stimulated oxygen migration in YBa2Cu3O7−δ superconducting bridges. The underlying methodology is rather simple and avoids sophisticated nanofabrication process steps and complex electronics. A patterned multiterminal transport bridge configuration allows us to electrically assess the directional counterflow of oxygen atoms and vacancies. Importantly, the emerging propagating front of current-dependent doping δ is probed in situ by optical microscopy and scanning electron microscopy. The resulting imaging techniques, together with photoinduced conductivity and Raman scattering investigations, reveal an inhomogeneous oxygen vacancy distribution with a controllable propagation speed permitting us to estimate the oxygen diffusivity. These findings provide direct evidence that the microscopic mechanism at play in electrical doping of cuprates involves diffusion of oxygen atoms with the applied current. The resulting fine control of the oxygen content would permit a systematic study of complex phase diagrams and the design of electrically addressable devices.The authors acknowledge the financial support from the Fonds de la Recherche ScientifiqueFNRS, Spanish Ministry of Economy and Competitiveness through the Severo Ochoa Programme for Centres of Excellence in R&D (SEV-2015- 0496), SUMATE project (RTI2018-095853-B-C21), cofinanced by the European Regional Development Fund, the COST programme NanoCoHybri (CA 16218), and from the Catalan Government with 2017 SGR 1519. The work of A. Fernańdez-Rodriǵuez has been done in the framework of the doctorate in Materials Science of the Autonomous University of Barcelona (UAB) and is supported by the Spanish Ministry of Economy (BES-2016-077310). The work of A. V. Silhanek is partially supported by the grant CDR J.0151.19 of the F.R.S.- FNRS. S. Blanco Alvarez, S. Melinte, and A. V. Silhanek acknowledge financial support through the grant PDR T.0106.16 of the F.R.S.-FNRS. S. Marinković acknowledges support from F.R.S.-FNRS (Research Fellowship ASP). B. Maiorov was supported by the U.S. DOE, Office of Science, BES, Materials Sciences and Engineering Division. The authors thank the ULiege Microscopy facility CAREM for the SEM investigations. G. Rius acknowledges the Ramon y Cajal grant RYC-2016-21412.Peer reviewe