MLIT scientist defended his PhD thesis on the numerical study of multiparameter models of Josephson structures On 12 September, MLIT researcher Maxim Bashashin successfully defended his thesis for the degree of Candidate of Physical and Mathematical Sciences at the Meshcheryakov Laboratory of Information Technologies. The thesis focused on the numerical study of superconducting processes and physical characteristics in multiparameter models of Josephson structures. The work was performed under the supervision of Elena Zemlyanaya, Doctor of Physical and Mathematical Sciences, Head of the Sector of Complex Physical Systems Computations at MLIT JINR. Ilhom Rahmonov, Candidate of Physical and Mathematical Sciences, Senior Researcher at the Sector of Nanostructure Physics of the Scientific Department of Condensed Matter Theory at the JINR Bogoliubov Laboratory of Theoretical Physics, was the scientific consultant of the work. Doctor of Physical and Mathematical Sciences, Professor of the Department of General Mathematics and Mathematical Physics at Tver State University Alexander Tsirulev and Doctor of Physical and Mathematical Sciences, Lead Researcher and Associate Professor at the «Keldysh Institute of Applied Mathematics» of the RAS Vladimir Sudakov were opponents. “Throughout his work at MLIT JINR, Maxim Bashashin has proven himself to be a qualified specialist in mathematical modeling, capable of elaborating algorithms and problem-oriented software packages and conducting the numerical analysis of multiparameter models of complex physical systems. I would especially like to highlight Maxim’s hard work and initiative, his desire to best perform assigned tasks, while offering his own approaches to solving them,” Elena Zemlyanaya emphasized. As experts point out, modern semiconductor microelectronics has reached its limits in terms of further reducing the size and enhancing the performance of computing systems based on this technology. On the other hand, superconducting microelectronics has demonstrated significant advances in recent decades, both in the theoretical understanding of the mechanisms of complex processes in such systems and in the development of technologies for their practical application. In this area, the scientific community is actively focusing on investigating fundamental laws that determine the characteristics of dynamic processes in Josephson structures of various types. The potential of using long Josephson junction (JJ) systems as the basis for quantum processors and superconducting computer memory is widely discussed in scientific circles. The Josephson effect is the foundation for generating and detecting coherent electromagnetic radiation in the terahertz range. The first of two models studied in Maxim Bashashin’s thesis describes one such long JJ system with capacitive and inductive coupling between adjacent junctions. The second model studied in the thesis is a model of an anomalous Josephson junction, namely, a ϕ0 junction of the superconductor-ferromagnet-superconductor type with spin-orbit coupling in a ferromagnetic layer. This model belongs to a field called superconducting spintronics, which has been actively developing over the past decade. Here, researchers are particularly interested in the possibility of controlling the magnetic moment by varying the superconducting current, as well as in the dynamics of superconducting processes under the influence of an external magnetic field. Both models are described by systems of nonlinear differential equations, the solutions of which depend on a large number of physical parameters. Investigating the properties and calculating the physical characteristics of the modeled structures is reduced to multiple numerical solutions of the mentioned systems of equations in a wide range of parameters. A key factor in achieving physically significant results more quickly is enhancing the performance of computer modeling through the implementation of parallelism and the use of computing systems available at MLIT Within his thesis, applying MPI and OpenMP parallel programming technologies, Maxim Bashashin created problem-oriented software packages for numerical research on computing systems with a parallel architecture of physical characteristics in the model of a stack of long JJs with capacitive and inductive coupling and for the investigation of the phenomenon of magnetization reversal in the ϕ0junction model with spin-orbit coupling in a ferromagnetic layer. The testing of the developed parallel programs conducted on the HybriLIT cluster and the “Govorun” supercomputer demonstrated that the maximum acceleration of computations in parallel mode compared to sequential computing was up to 10 times for the problem of modeling current-voltage characteristics (CVCs) in the system of long JJs and up to 30 times for the problem of modeling the magnetization reversal in the ϕ0 junction. The numerical modeling of the current-voltage characteristics of the system of long coupled JJs showed that even weak inductive and capacitive coupling between adjacent JJs resulted in the emergence of new fluxon states, which is reflected in the CVC structure and the intensity of electromagnetic radiation. The numerical study of the ϕ0junction model with spin-orbit coupling in a ferromagnetic layer revealed patterns and the influence of a number of factors on the periodic structure of the parameter regions where the magnetization reversal occurs. The developed software packages are available for free use in the JINRLIB software library and are currently being employed for the further investigation of models of Josephson structures of various configurations. During the discussion of the thesis, it was noted that the methods developed in the thesis could be applied to the numerical study of photonics and biophysics models. Maxim Bashashin became involved in the numerical investigation of Josephson structures in 2015, being a student at Dubna State University. This research was conducted in close collaboration with scientists from the Bogoliubov Laboratory of Theoretical Physics. According to his colleagues, Maxim Bashashin has proven himself to be a competent specialist and has made a considerable contribution to obtaining a number of physical results crucial for understanding the mechanisms of influence of various factors on the behavior of Josephson junctions and the structure of the corresponding physical characteristics. In 2016, Maxim Bashashin graduated with honors from Dubna State University with a master’s degree in system analysis and management. In 2023-2024, he passed candidate minimum exams at the same university. Maxim Bashashin currently works as a researcher at the Sector of Complex Physical Systems Computations of the Scientific Department of Computational Physics at MLIT JINR, where he completed his thesis. He continues his research in the field of Josephson structure modeling, as well as in other areas related to the computer analysis of complex physical systems. In addition to his fruitful scientific activity, Maxim Bashashin teaches at the MSU branch in Dubna within the new Applied Mathematics and Computer Science course (program «Data Processing Methods and Technologies in Heterogeneous Computing Environments») and at Dubna University; he is also involved in the HybriLIT group.
