Simulation of microscopic defect formation in layered high-temperature superconducting composites by exposure to ultrashort laser pulses Текст научной статьи по специальности «Электротехника, электронная техника, информационные технологии»

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Simulation of microscopic defect formation in layered high-temperature superconducting composites by exposure to ultrashort laser pulses

I. Martirosian, S. Pokrovskii, I. Rudnev

National Research Nuclear University MEPHI, Kashorskoye shosse, 31, Moscow, Russia Main author email address: mephizic@gmail.com

At present, the most important step in the production of high-temperature superconducting (HTS) materials with high critical current density Jc is the creation of effective magnetic flux pinning centers in the HTS structure. For the HTS, this problem is particularly acute due to the insufficient efficiency of pinning on natural defects and the large contribution of thermal fluctuations at temperatures close to the critical one (Tc). In this regard, the tasks of both determining the conditions for increasing the critical current of materials (the type of defects, their concentration and dispersion) and finding ways to control the creation of additional artificial defects that would act as magnetic flux pinning centers are topical. The main tools for controlled actions on superconductors, leading to a change in their properties, were the introduction of nanosized additives in the solid-state synthesis of high-temperature superconductors [1], surface modification by scratching [2, 3], antidot arrays etching [4, 5], and substrate modification [6 -8], deposition of magnetic islands [9], irradiation with high-energy particles (protons [10], neutrons [11], electrons [12]). Meanwhile, despite some progress in increasing Jc using laser drilling, a number of issues remain unresolved both in terms of optimizing the creating mi-crodefects process and analyzing the mechanisms of defect formation in HTS composites using ultrashort laser pulses.

In this work, pulsed laser action is considered as a method for forming a defect structure of superconducting composites based on REBCO (REBa2Cu3O7-x, where RE is a rare earth element). A study and numerical analysis of the formation of a defect structure in REBCO HTS films under ultrashort laser irradiation has been carried out. In particular, various laser action regimes and the corresponding local thermal processes leading to heating of the film, melting, and evaporation of the superconducting and the substrate materials are considered. The dependences of the diameter and depth of the defect on the laser radiation energy in a wide energy range (from 50 to 900 nJ) are studied, the features of defect formation are shown for sequences of 2 to 20 laser radiation pulses at one point at different focusing radius of laser radiation (from 1.5 to 3 ^m). In the present work, it is shown that the thermal processes occurring under laser irradiation naturally determine the parameters (type, shape, size) of effective pinning centers, and, consequently, the most important fundamental characteristics of HTS materials.

The reported study was funded by RFBR, project number 20-08-00811, and research project № 20-38-90144 (I.V. Martirosian)

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