First-principles study of the superconductivity in MgB2 bulk and in its bilayer thin film based on electron–phonon coupling

• DOI: 10.1016/j.physc.2014.11.006
• Publication Date: 2014-11-29T20:25:25Z
• Authors: T. Morshedloo; M.R. Roknabadi; M. Behdani
• Keywords: Density of states; Dispersion relation

Abstract In this paper, phonon-mediated superconductivity has been investigated in MgB 2 bulk structure and bilayer thin film by using first-principles calculations. The electronic band structure, total and partial density of states (DOS and PDOS), phonon dispersion, isotropic Eliashberg function α 2 F ( ω ), and electron–phonon coupling have been calculated within the framework of density functional theory (DFT). Our results indicate that holes at the top of boron σ bands mainly and holes in the boron π band partially contribute to formation of coupled holes in superconductivity state. The density of states at the Fermi energy level is increased for MgB 2 bilayer with respect to its bulk structure. According to the phonon dispersion and Eliashberg function curves, coupling considerably occurs between holes at the top of the boron σ band by means of optical phonon mode for both structures. This phonon mode has the E 2g symmetry at the Г point. We obtain electron–phonon coupling constants of 0.74 and 0.91 for bulk and bilayer structures, respectively. By using the Allen–Dynes formula, we estimate superconducting transition temperature T C of 40 K for bulk and 48 K for the thin film.