Low-energy plasmonic structure in CaC6

Abstract

The low-energy dielectric properties of CaC 6 -a representative graphite intercalated compound (GIC)-were investigated by ab initio time-dependent density functional theory calculations with full inclusion of local field effects. The calculations predict the existence of several kinds of plasmons in CaC 6 with energy below 10 eV. The mode with the largest energy is a conventional "πp" mode strongly dispersing in the hexagonal basal plane and almost nondispersing in the perpendicular direction. In the 2.3-3 eV energy range, we find a long-lived intraband plasmon with negative (positive) dispersion with momentum transfer in (perpendicular to) the basal plane. In the 0-1.5 eV energy range, a mode with linear soundlike dispersion along all three high-symmetry directions is observed. All the three modes present strong anisotropy originated from the band structure. The physical origin of these excitation modes is discussed in terms of intra-and interband transitions. The crucial role of local field effects in the propagation of the two lowest-energy modes at large momentum transfers and in the determination of its dispersion over extended momentum-transfer region is analyzed.

Interplay between structure and electronic properties of layered transition-metal dichalcogenides: Comparing the loss function of1Tand2Hpolymorphs

“…The latter can act to screen the repulsion between the former, resulting in the appearance of a plasma mode with a soundlike dispersion. This is, for instance, what has been proved in MgB 2 [33], which has two bands with π (fast carriers) and σ (slow carriers) character that are metallic (i.e., cross the Fermi energy) or in other materials such as CaC 6 [34], Pb [35], and Pd [36]. With respect to this, 2H-TMD are similar to MgB 2 since the d z 2 and p z bands can play the same role of the σ and π bands, respectively.…”

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

“…57 We relay the appearance of this peak to the existence of a low-energy acoustic plasmon, also predicted to exist on base of the first-principles calculations in other systems such as MgB 2 and Pd. 31,58 Previously such kind of plasmon was intensively investigated in various layered systems [23][24][25][26][27][28][29][30][31][32][33][34] and other materials with two kinds of carriers at the Fermi level. [59][60][61][62][63][64] The appearance of this plasmon is related to the presence of two kinds of charge carriers characterized by different maximal Fermi velocity components in a given direction in the energy bands crossing the Fermi surface.…”

“…22 At the same time, there is a rich literature on plasmons in other layered systems like semiconductor superlattice structures, [23][24][25][26][27][28] high-T c oxides, 29,30 MgB 2 , 31 other layered superconductors, 32,33 and intercalated graphite. 34 In these studies it was demonstrated that the presence of the layered structure leads to strong modifications in the plasmon spectrum in comparison with that of a homogeneous three-dimensional electron gas. Thus in addition to the conventional bulk plasmon the existence in such systems of an additional mode with characteristic soundlike dispersion was demonstrated.…”

Effects of5delectrons and spin-orbit interaction on the characteristics of bulk plasmons in lead

“…Very often, these transitions play an important role in the formation of excitation spectrum; in particular, of plasmon properties. For instance, the intraband transitions within several partly occupied energy bands induce low-energy plasmons with characteristic sound-like dispersion in some materials [20,21,[33][34][35]. The interband transitions give rise to a strong redshift of the Ag plasmon frequency [36,37] or to a negative momentum dispersion [38,39] of the plasmon in heavy alkali metals [40,41].…”

“…The interband transitions give rise to a strong redshift of the Ag plasmon frequency [36,37] or to a negative momentum dispersion [38,39] of the plasmon in heavy alkali metals [40,41]. Moreover, these transitions dominate the energy-loss landscape in the low-energy-transfer domain in many materials like MgB 2 [15,16], intercalated graphite [35,42], transition-metal dichalcogenides [20,21,[43][44][45], lead [31], and Heusler compounds [46].…”