Microscopic Origin of the Abnormal Elastic Behavior Accompanying the Superconducting Transition in Nb3Sn Crystals: an Extended Ab Initio Study

As a promising next-generation material for superconducting radiofrequency cavities, superconducting Nb3Sn, once developed for fabricating a high-field magnet, has attracted tremendous research interest due to the significant potential for both compact and large scale accelerator applications. However, the intrinsic physical origin, especially at atomic and electronic scale, of the abnormal elastic behavior accompanying the superconducting transition in Nb3Sn crystals is still controversial and not fully understood yet. Through an extended atomic and electronic modelling of electronic structure evolution arising from the perturbation of lattice strain and temperature, we proposed an analytical model for depicting the abnormal temperature-dependent elastic constants and transition resistivities of superconducting Nb3Sn. The extended ab initio modeling takes into account the interaction of the d electrons with the strain, the strain-modulated electronic structure evolution and the accompanied variations in the density of states at the Fermi level, and the competition between the lattice contribution and the electron contribution in governing the abnormal elastic response along with the superconducting transition of Nb3Sn. The model predictions of the elastic constants and the superconducting phase transition resistivities of single crystal and polycrystalline Nb3Sn qualitatively agree with the experimental observations. The extended ab initio studies indicate the abnormal changes in the elastic properties and the transition resistivity response characteristics are intrinsically correlated, the contribution arising from the d-band electrons determines the cross-scale abnormal elastic behavior accompanying the superconducting transition in Nb3Sn crystals.