Abstract
The effect of hydrostatic pressure on superconductivity of hexagonal bulk MgB2 was investigated using the first-principles calculations. The calculations were performed based on the density functional theory employing the very recently developed EPW code incorporated in Quantum ESPRESSO computational package. The phonon density of states (PhDOS), isotropic Eliashberg function α2F(ω), the superconducting gap along real and imaginary frequency axes, the electron-phonon coupling constant λ, and the superconducting critical temperature Tc were computed within the general framework of Eliashberg formalism. The results show that hydrostatic pressure enhances superconductivity of the material. At equilibrium, where the hydrostatic pressure of the system is almost zero, the calculated Tc value is 35.67 K. It is relatively nearer to the experimental value of 39 K. The slight underestimation is attributed to the LDA-DFT approximation employed. This value is enhanced to around 95 K at hydrostatic pressure of 6500 kbar and then starts to decrease slowly. We emphasize that our approach to lattice strain engineering, with the target of enhancing Tc as demonstrated in this work, can be applied to various strain-engineering problems in other functional materials.
Highlights
In strongly-correlated systems, the many-body ground state that emerges can have exotic and unexpected properties
First principle calculations were performed within the local density approximation (LDA) to density functional theory (DFT)14–18 as implemented in Quantum ESPRESSO computational package
Based on Migdal–Eliashberg theory formulated for strongly coupled anisotropic superconductors, we have investigated the effect of hydrostatic pressure on superconductivity of bulk hexagonal MgB2
Summary
In strongly-correlated systems, the many-body ground state that emerges can have exotic and unexpected properties. EPW is a program written in Fortran for calculating the electron-phonon coupling constant in periodic systems using density functional perturbation theory and maximally localized Wannier functions. It is fully itegrated with Quantum ESPRESSO computational package.. EPW makes use of a real-space formulation and combines the Kohn–Sham electronic eigenstates and the vibrational eigenmodes provided by the Quantum-ESPRESSO package with the maximally localized Wannier functions provided by the wannier package in order to generate electron-phonon matrix elements on arbitrarily dense Brillouin zone grids using a generalized Fourier interpolation It can calculate electron-phonon interaction self-energies, electron-phonon spectral functions, superconducting critical temperatures, superconductig gap prameters, and the total as well as the mode-resolved electron-phonon coupling strengths.
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