The effect of strain and pressure on the electron-phonon coupling and superconductivity in MgB2—Benchmark of theoretical methodologies and outlook for nanostructure design

Abstract

Different theoretical methodologies are employed to investigate the effect of hydrostatic pressure and anisotropic stress and strain on the superconducting transition temperature (T c ) of MgB 2 . This is done both by studying Kohn anomalies in the phonon dispersions alone and by explicit calculation of the electron-phonon coupling. It is found that increasing pressure suppresses T c in all cases, whereas isotropic and anisotropic strain enhances the superconductivity. In contrast to trialed epitaxial growth that is limited in the amount of achievable lattice strain, we propose a different path by co-deposition with ternary diborides that thermodynamically avoid mixing with MgB 2 . This is suggested to promote columnar growth that can introduce strain in all directions.

Superlattices, Bonding-Antibonding, Fermi Surface Nesting, and Superconductivity

“…We have demonstrated, along with others [35][36][37][38], that the accuracy of DFT results depends on calculation setup choices, such as the density of k-grid values, cut off energies or radii, pseudopotentials, symmetry assumptions, convergence tolerances, and other resolution-related factors specific to a compound's structure. Variability of results is to be expected for discrete DFT calculations given the variety of possible physical assumptions and setup conditions for calculations, in much the same way as a calculation on integral numbers is approximated by vertical rectangular areas of different widths.…”

“…For example, valuable insights on materials including superconductors have also been gained from questioning the limitations of DFT [35][36][37][38][39][40][41]. DFT procedures normally make use of linear approximations [3][4][5], even though linearity may not properly represent physical realities, particularly for superconductors.…”