Giant anharmonicity and non-linear electron-phonon coupling in MgB${}_2$; A combined first-principles calculations and neutron scattering study

Abstract

We report first-principles calculations of the electronic band structure and lattice dynamics for the new superconductor MgB${}_2$. The excellent agreement between theory and our inelastic neutron scattering measurements of the phonon density of states gives confidence that the calculations provide a sound description of the physical properties of the system. The numerical results reveal that the in-plane boron phonons (with E${}_{2g}$ symmetry) near the zone-center are very anharmonic, and are strongly coupled to the partially occupied planar B $\ddot{I}ƒ$ bands near the Fermi level. This giant anharmonicity and non-linear electron-phonon coupling is key to explaining the observed high T${}_c$ and boron isotope effect in MgB${}_2$

In this revised version (to appear in PRL) we also discuss the boron isotope effect. Please visit http://www.ncnr.nist.gov/staff/taner/mgb2 for details