Role of band structure and local-field effects in the low-energy collective electronic excitation spectra of 2H-NbSe2

M.N. FARAGGI; A. ARNAU; V.M. SILKIN

PHYSICAL REVIEW B

AMER PHYSICAL SOC

Lugar: New York; Año: 2012 vol. 86 p. 1 - 10

1098-0121

We present a study of the electron dynamics in the layered compound 2H-NbSe2. First-principles calculationsare used to obtain the band structure employed in the evaluation of the loss function with inclusion of local-field(LF) effects. Two different symmetry directions [(100) and (010)] were explored in the hexagonal basal plane.In both cases, a low-energy charge-carrier plasmon (CCP) at ∼1 eV presenting a negative dispersion over a widemomentum transfer range is found, in agreement with recent experimental results [Wezel et al., Phys. Rev. Lett.107, 176404 (2011)]. On the contrary, in the (001) perpendicular direction, the CCP has negative dispersion atsmall momenta only, presenting strong positive dispersion at larger momenta. Our calculations reveal that thisbehavior can be explained without invoking many-body effects, as long as band structure effects are properlyincluded in the evaluation of the excitation spectra. In addition to this CCP mode, we find another one with anarclike oscillating dispersion along the perpendicular direction, as well as the appearance of a CCP replica athigh momenta due to LF effects.