Effect Of Strain On Critical Transition Temperature Of MgB₂ Superconductor

Because of their excellent current-carrying capacity and high critical magnetic field,superconducting materials have broad application prospects in high-tech fields such as power transmission,medical technology,and nuclear fusion devices and so on.Since most superconducting materials work in an environment of extremely low temperature,high current and strong magnetic field,the mechanical properties in this extreme environment have become a key factor restricting the safe and stable operation of various superconducting equipment.Previous studies have shown that the mechanical deformation of superconducting materials can have a significant effect on the superconducting critical transition temperature(T_c),but there are few studies on the effect of strain on the T_c of superconducting materials,especially on the relationship between uniaxial strain and T_c.This paper takes MgB₂ superconducting material as the research object,based on first-principles density functional theory(DFT)and Mc Millan's superconductivity calculation formula,with the help of Materials Studio and Quantum Espresso,two first-principles calculation software,mainly research the change of T_c value of Mg B₂ superconducting material under hydrostatic pressure and uniaxial strain.Then this paper calculated some physical properties of Mg B₂ under uniaxial strain,including the Debye temperature,electron-phonon coupling parameter,critical transition temperature,elastic constant,elastic anisotropy,band structure,electronic density of states,Fermi surface structure,differential charge density,phonon dispersion spectrum,phonon density of states,and Eliashberg spectral and other properties.The relationship between strain and these properties are analyzed,and then the deep reasons for the change of T_c of Mg B₂ superconducting material caused by strain are explored.This paper calculates that the a-axis tensile strain can effectively increase the T_c value of Mg B₂.When the tensile strain is 1%,the T_c value increases to 49.7K,while the T_c value changes little under c-axis tensile and compressive strain.In addition,the calculation shows that the effect of uniaxial strain on T_c and some physical properties of Mg B₂ is greater than that of uniaxial strain on c-axis,which is mainly due to the layered structure of Mg B₂ and the effect of B atomic layer on its superconductivity.The results show that the density of states at Fermi level and the frequency of E_2g phonon mode at G point in Mg B₂ decrease under a-axis tensile strain,but the change of density of States is very small.The increase of TC is mainly due to the decrease of E_2g phonon mode frequency and the enhancement of electro acoustic coupling.The work in this paper has some theoretical significance for the preparation of Mg B₂ with higher T_c and the study of the effect of strain on T_c.