Ab initio investigation of collective charge excitations in MgB2 -: art. no. 057001

A sharp collective charge excitation is predicted in MgB2 at similar to2.5 eV for q perpendicular to the boron layers, based on an all-electron analysis of the dynamical density response within time-dependent density functional theory. This novel excitation, consisting of coherent charge fluctuation between Mg and B sheets, induces an abrupt plasma edge in the experimentally observable reflectivity. The existence of this mode reflects the unique electronic structure of MgB2 that is also responsible for strong electron-phonon coupling. By contrast, the acoustic plasmon, recently suggested to explain the high T-c, is not realized when realistic transition strengths are incorporated.