Experimental Observation of s -Component of Superconducting Pairing in Thin Disordered HTSC Films Based on YBCO
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Experimental Observation of s-Component of Superconducting Pairing in Thin Disordered HTSC Films Based on YBCO A. V. Antonova, A. I. El’kinaa, V. K. Vasilieva, M. A. Galina, D. V. Masterova, A. N. Mikhaylovb, S. V. Morozova, S. A. Pavlova, A. E. Parafina, b, D. I. Tetelbaumb, S. S. Ustavschikova, b, P. A. Yunina, b, and D. A. Savinova, b, * a
Institute for Physics of Microstructures, Russian Academy of Sciences, Nizhny Novgorod, 603950 Russia b Lobachevsky State University, Nizhny Novgorod, 603950 Russia *e-mail: [email protected] Received March 26, 2020; revised March 26, 2020; accepted April 2, 2020
Abstract—The original research results for thin disordered HTSC films based on YBCO are presented in this article. Several experiments have been carried out to confirm a theoretical prediction that the s-phase of superconducting pairing in disordered d-type superconductors can occur with a gradual decrease in the mean free path. The YBa2Cu3O7 – x films are used as samples which possess a d-type of superconducting state that was experimentally confirmed. A gradual decrease in the mean free path was achieved by both thermal annealing and ion irradiation. The experiments included measurements of temperature dependence of the London penetration depth λ and resistive studies. Keywords: high-temperature superconductors, thin films, disorder, ion irradiation, thermal annealing, London penetration depth, resistance measurements DOI: 10.1134/S1063783420090036
1. INTRODUCTION In several recent years, a vivid splash in the studies of high-temperature superconductors (HTSCs) with a high degree of disorder (see, e.g., [1–4]) has been observed. The interest in them is determined by the fact that the manifestation of quite unusual properties of such materials is possible near the superconductor– normal metal (or superconductor–isolator) transition. In particular, it has been experimentally found that the electron transport in the nonsuperconducting state of the films of YBCO containing a nanohole lattice is executed not by individual electrons but by Cooper pairs [1]. Also, an unusual characteristic feature of disordered HTSC materials is the possibility of formation of the s-phase of superconductive pairing upon a gradual increase in the degree of disorder in the samples, which was recently theoretically predicted [2, 3]. Moreover, the properties of such materials in an external magnetic field H turn out to be even more mysterious, thus, the temperature dependence of the upper critical field Hc2(T) turns out to be monotonically increasing, which leads to the possibility of stimulation of superconductivity by means of applying H [4], while, commonly, an external magnetic field always suppresses the critical temperature Tc. Some other abnormal characteristic features of the phase diagrams
on the external magnetic field H–temperature T plane were experimentally studied in our recent works for thin films of YBa2Cu3O7 – x with different degrees of disorder [5, 6]. The disorder in the samples was gradually varied by io
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