Giant Anharmonicity and Nonlinear Electron-Phonon Coupling inMgB2: A Combined First-Principles Calculation and Neutron Scattering Study

Abstract

First-principles calculations of the electronic band structure and lattice dynamics for the new superconductor $\mathrm{MgB}{}_2$ are carried out and found to be in excellent agreement with our inelastic neutron scattering measurements. The numerical results reveal that the $E_{2g}$ in-plane boron phonons near the zone center are very anharmonic and strongly coupled to the planar B $\sigma$ bands near the Fermi level. This giant anharmonicity and nonlinear electron-phonon coupling is key to quantitatively explaining the observed high $T_c$ and boron isotope effect in $\mathrm{MgB}{}_2$.