2,966 research outputs found
Collective Modes of Massive Dirac Fermions in Armchair Graphene Nanoribbons
We report the plasmon dispersion characteristics of intrinsic and extrinsic
armchair graphene nanoribbons of atomic width N = 5 using a p_z-orbital tight
binding model with third-nearest-neighbor (3nn) coupling. The coupling
parameters are obtained by fitting the 3nn dispersions to that of an extended
Huckel theory. The resultant massive Dirac Fermion system has a band gap E_g
\approx 64 meV. The extrinsic plasmon dispersion relation is found to approach
a common dispersion curve as the chemical potential increases, whereas
the intrinsic plasmon dispersion relation is found to have both energy and
momentum thresholds. We also report an analytical model for the extrinsic
plasmon group velocity in the q \rightarrow 0 limit
Plasmon dispersion in semimetallic armchair graphene nanoribbons
The dispersion relations for plasmons in intrinsic and extrinsic semimetallic
armchair graphene nanoribbons (acGNR) are calculated in the random phase
approximation using the orthogonal p_z-orbital tight binding method. Our model
predicts new plasmons for acGNR of odd atomic widths N=5,11,17,... Our model
further predicts plasmons in acGNR of even atomic width N=2,8,14,... related to
those found using a Dirac continuum model, but with different quantitative
dispersion characteristics. We find that the dispersion of all plasmons in
semimetallic acGNR depends strongly on the localization of the p_z electronic
wavefunctions. We also find that overlap integrals for acGNR behave in a more
complex way than predicted by the Dirac continuum model, suggesting that these
plasmons will experience a small damping for all q not equal to 0. Plasmons in
extrinsic semimetallic acGNR with the chemical potential in the lowest
(highest) conduction (valence) band are found to have dispersion
characteristics nearly identical to their intrinsic counterparts, with
negligible differencs in dispersion arising from the slight differences in
overlap integrals for the interband and intraband transitions.Comment: 8 pages, 9 figure
A theoretical model for single molecule incoherent scanning tunneling spectroscopy
Single molecule scanning tunneling spectroscopy (STS), with dephasing due to
elastic and inelastic scattering, is of some current interest. Motivated by
this, we report an extended Huckel theory (EHT) based mean-field
Non-equilibrium Green's function (NEGF) transport model with electron-phonon
scattering treated within the self-consistent Born approximation (SCBA).
Furthermore, a procedure based on EHT basis set modification is described. We
use this model to study the effect of the temperature dependent dephasing, due
to low lying modes in far-infrared range for which hw<<kT, on the resonant
conduction through highest occupied molecular orbital (HOMO) level of a phenyl
dithiol molecule sandwiched between two fcc-Au(111) contacts. Furthermore, we
propose to include dephasing in room temperature molecular resonant conduction
calculations.Comment: 12 pages, 5 figure
- …