A sharp collective charge excitation was predicted in MgB2 at approximately 2.5eV for q perpendicular to the B layers, based on an all-electron analysis of the dynamic 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 was also responsible for strong electron-phonon coupling. By contrast, the acoustic plasmon, recently suggested to explain the high TC, was not realized when realistic transition strengths were incorporated.

Ab initio Investigation of Collective Charge Excitations in MgB2. W.Ku, W.E.Pickett, R.T.Scalettar, A.G.Eguiluz: Physical Review Letters, 2002, 88[5], 057001 (3pp)