1,092 research outputs found
Screening and plasmons in pure and disordered single- and bilayer black phosphorus
We study collective plasmon excitations and screening of disordered single-
and bilayer black phosphorus beyond the low energy continuum approximation. The
dynamical polarizability of phosphorene is computed using a tight-binding model
that properly accounts for the band structure in a wide energy range.
Electron-electron interaction is considered within the Random Phase
Approximation. Damping of the plasmon modes due to different kinds of disorder,
such as resonant scatterers and long-range disorder potentials, is analyzed. We
further show that an electric field applied perpendicular to bilayer
phosphorene can be used to tune the dispersion of the plasmon modes. For
sufficiently large electric field, the bilayer BP enters in a topological phase
with a characteristic plasmon spectrum, which is gaped in the armchair
direction.Comment: 9 pages, 9 figure
Landau Level Spectrum of ABA- and ABC-stacked Trilayer Graphene
We study the Landau level spectrum of ABA- and ABC-stacked trilayer graphene.
We derive analytic low energy expressions for the spectrum, the validity of
which is confirmed by comparison to a \pi -band tight-binding calculation of
the density of states on the honeycomb lattice. We further study the effect of
a perpendicular electric field on the spectrum, where a zero-energy plateau
appears for ABC stacking order, due to the opening of a gap at the Dirac point,
while the ABA-stacked trilayer graphene remains metallic. We discuss our
results in the context of recent electronic transport experiments. Furthermore,
we argue that the expressions obtained can be useful in the analysis of future
measurements of cyclotron resonance of electrons and holes in trilayer
graphene.Comment: 10 pages, 8 figure
Effect of Point Defects on the Optical and Transport Properties of MoS2 and WS2
Imperfections in the crystal structure, such as point defects, can strongly
modify the optical and transport properties of materials. Here, we study the
effect of point defects on the optical and DC conductivities of single layers
of semiconducting transition metal dichalcogenides with the form S,
where =Mo or W. The electronic structure is considered within a six bands
tight-binding model, which accounts for the relevant combination of
orbitals of the metal and orbitals of the chalcogen . We use the
Kubo formula for the calculation of the conductivity in samples with different
distributions of disorder. We find that and/or S defects create mid-gap
states that localize charge carriers around the defects and which modify the
optical and transport properties of the material, in agreement with recent
experiments. Furthermore, our results indicate a much higher mobility for
-doped WS in comparison to MoS
Self-Consistent Screening Approximation for Flexible Membranes: Application to Graphene
Crystalline membranes at finite temperatures have an anomalous behavior of
the bending rigidity that makes them more rigid in the long wavelength limit.
This issue is particularly relevant for applications of graphene in nano- and
micro-electromechanical systems. We calculate numerically the height-height
correlation function of crystalline two-dimensional membranes,
determining the renormalized bending rigidity, in the range of wavevectors
from \AA till 10 \AA in the self-consistent screening
approximation (SCSA). For parameters appropriate to graphene, the calculated
correlation function agrees reasonably with the results of atomistic Monte
Carlo simulations for this material within the range of from
\AA till 1 \AA. In the limit our data for the
exponent of the renormalized bending rigidity is compatible with the previously known analytical results for the
SCSA . However, this limit appears to be reached only for
\AA whereas at intermediate the behavior of
cannot be described by a single exponent.Comment: 5 pages, 4 figure
Thermodynamics of quantum crystalline membranes
We investigate the thermodynamic properties and the lattice stability of
two-dimensional crystalline membranes, such as graphene and related compounds,
in the low temperature quantum regime . A key role is played by
the anharmonic coupling between in-plane and out-of plane lattice modes that,
in the quantum limit, has very different consequences than in the classical
regime. The role of retardation, namely of the frequency dependence, in the
effective anharmonic interactions turns out to be crucial in the quantum
regime. We identify a crossover temperature, , between classical and
quantum regimes, which is K for graphene. Below , the
heat capacity and thermal expansion coefficient decrease as power laws with
decreasing temperature, tending to zero for as required by the
third law of thermodynamics.Comment: 13 pages, 1 figur
Reply to 'Comment on "Thermodynamics of quantum crystalline membranes"'
In this note, we reply to the comment made by E.I.Kats and V.V.Lebedev
[arXiv:1407.4298] on our recent work "Thermodynamics of quantum crystalline
membranes" [Phys. Rev. B 89, 224307 (2014)]. Kats and Lebedev question the
validity of the calculation presented in our work, in particular on the use of
a Debye momentum as a ultra-violet regulator for the theory. We address and
counter argue the criticisms made by Kats and Lebedev to our work.Comment: 5 pages, 4 figure
Plasmon Spectrum of Single Layer Antimonene
The collective excitation spectrum of two-dimensional (2D) antimonene is
calculated beyond the low energy continuum approximation. The dynamical
polarizability is computed using a 6-orbitals tight-binding model that properly
accounts for the band structure of antimonene in a broad energy range.
Electron-electron interaction is considered within the random phase
approximation. The obtained spectrum is rich, containing the standard
intra-band 2D plasmon and a set of single inter-band modes. We find that
spin-orbit interaction plays a fundamental role in the reconstruction of the
excitation spectrum, with the emergence of novel inter-band branches in the
continuum that interact with the plasmon.Comment: 8 pages, 9 figures, accepted by Phys. Rev.
Effect of moir\'e superlattice reconstruction in the electronic excitation spectrum of graphene-metal heterostructures
We have studied the electronic excitation spectrum in periodically rippled
graphene on Ru(0001) and flat, commensurate graphene on Ni(111) by means of
high-resolution electron energy loss spectroscopy and a combination of density
functional theory and tight-binding approaches. We show that the periodic
moir\'e superlattice originated by the lattice mismatch in graphene/Ru(0001)
induces the emergence of an extra mode, which is not present in
graphene/Ni(111). Contrary to the ordinary intra-band plasmon of doped
graphene, the extra mode is robust in charge-neutral graphene/metal contacts,
having its origin in electron-hole inter-band transitions between van Hove
singularities that emerge in the reconstructed band structure, due to the
moir\'e pattern superlattice.Comment: Supplemental materials available at
http://www.theorphys.science.ru.nl/people/yuan
Polarization of graphene in a strong magnetic field beyond the Dirac cone approximation
In this paper we study the excitation spectrum of graphene in a strong
magnetic field, beyond the Dirac cone approximation. The dynamical
polarizability is obtained using a full -band tight-binding model where
the effect of the magnetic field is accounted for by means of the Peierls
substitution. The effect of electron-electron interaction is considered within
the random phase approximation, from which we obtain the dressed polarization
function and the dielectric function. The range of validity of the Landau level
quantization within the continuum approximation is studied, as well as the
non-trivial quantization of the spectrum around the Van Hove singularity. We
further discuss the effect of disorder, which leads to a smearing of the
absorption peaks, and temperature, which activates additional inter-Landau
level transitions induced by the Fermi distribution function.Comment: 11 pages, 10 figure
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