Study on the relationship between uniaxial strain and critical transition temperature of MgB 2 based on first-principles

It has been indicated the critical transition temperature ( T c ) of MgB 2 decreases with the increase of hydrostatic pressure, but this is a comprehensive T c change after the multiaxial strain, and the influence of strain on T c is not fully understood. In this paper, based on the McMillan superconducting calculation formula and the first-principles density functional theory, the T c change and the properties of MgB 2 such as energy band, Fermi surface, differential charge density, and phonon dispersion under uniaxial strain were studied, and the relationship between uniaxial strain and these properties was analyzed. The calculated T c of MgB 2 at zero strain was 38.35 K, which is in good agreement with the experimental value of 39 K. When the a -axis strain was 1%, the T c value could increase to 49.7 K, and there was a further improvement trend. When the a -axis compression strain was −1%, T c decreases to 31.52 K. When the c -axis tension–compression strain was applied, the change of T c value was small. Further analysis showed that the impact of a -axis strain on the differential charge density, electronic band structure, phonon dispersion, and other properties of MgB 2 was significantly greater than that of c -axis strain, and the influence of these properties on T c was discussed. The work in this paper has certain theoretical and guiding significance for preparing MgB 2 with higher T c and the study of the effect of uniaxial strain on T c of superconducting materials.