Electromechanical coupling in high-pressured superconducting Nb3Sn: analytical and simulation models

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Based on molecular dynamics (MD) simulations of Nb3Sn crystals under high pressure, a physics-based trans-scale model of the superconducting transition of high-pressure Nb3Sn is proposed. This model investigates the electromechanical coupling effect of Nb3Sn and discusses the effect of grain boundary deformation on electromechanical coupling through simulations. The simulated results demonstrate that the strain-induced electronic structure evolution and accompanying variations in the density of states (DOS) at the Fermi surface control the superconducting transition of single-crystal Nb3Sn. This effect is amplified by the stress concentrations at the grain boundary intersections, leading to the obviously different electromechanical responses of high-pressure single-crystal and polycrystal Nb3Sn. It was further found that the electromechanical coupling effect in Nb3Sn was scale coupled, including a strain-regulated electronic structure, grain boundary contours of strained Nb3Sn at the atomic scale, local atom stress distribution, and intrinsic connections between the strain-modulated superconducting and normal-state transport properties (at the macroscale level). The linkage between the micro-meso-macro-scales was qualitatively reproduced by the proposed model, where the three principal strain components and their differences represent the response-controlling parameters. The grain boundary zone was critical to further determine the reversible–irreversible transition of the electromechanical coupling effects in Nb3Sn. The proposed analytical and simulation models provided important theoretical guidance for understanding the empirical relation obtained experimentally. Additionally, they presented a method for the parameterization of electromechanical coupling in Nb3Sn.