1,664 research outputs found
Optical properties of graphene: the Fermi liquid approach
Optical properties of two-dimensional massless Dirac fermions are considered
by the formalism of pseudospin precession equations which provides an easy and
natural semiphenomenological way to include correlation effects. It is shown
that the latter are negligible, with the only assumption that the system under
consideration is normal Fermi liquid. This result probably explains recent
experimental data on the universal optical conductivity of graphene (Nair R. R.
et al, Science 320 (2008) 1308).Comment: 3 page
Graphene: carbon in two dimensions
Carbon is one of the most intriguing elements in the Periodic Table. It forms
many allotropes, some being known from ancient times (diamond and graphite) and
some discovered ten to twenty years ago (fullerenes, nanotubes). Quite
interestingly, the two-dimensional form (graphene) has been obtained only very
recently, and immediately attracted great deal of attention. Electrons in
graphene, obeying linear dispersion relation, behave like massless relativistic
particles, which results in a number of very peculiar electronic properties
observed in this first two-dimensional material: from an anomalous quantum Hall
effect to the absence of localization. It also provides a bridge between
condensed matter physics and quantum electrodynamics and opens new perspectives
for carbon-based electronics.Comment: Review paper on graphene, a bit shortened in comparison with the
published version (some figures are changed or omitted
Coulomb drag in graphene single layers separated by a thin spacer
Motivated by very recent studies of Coulomb drag in grahene-BN-graphene
system we develop a theory of Coulomb drag for the Fermi liquid regime, for the
case when the ratio of spacer thickness to the Fermi wavelength of
electrons is arbitrary. The concentration () and thickness dependence of the
drag resistivity is changed from for the thick spacer to
for the thin one.Comment: final version; more details on the solution of electrostatic problem
and some references are adde
Electron self-trapping and fluctuation density-of-states tail at the critical point
We consider electron self-trapping due to its interaction with
order-parameter fluuctuations at the second-order phase-transition or critical
point (for example, at the Curie temperature in magnetic or ferroelectric
semiconductors). Using Feynman path integral approach the autolocalization
energy and the size of the self-trapped state (fluctuon) are estimated. It is
shown that the fluctuon states are connected with the Lifshitz tail of the
electron density-of-states, the parameters of this tail being determined by the
critical exponents.Comment: 4 pages, revtex4, Phys. Rev. B, accepte
An dynamical-mean-field-theory investigation of specific heat and electronic structure of and -plutonium
We have carried out a comparative study of the electronic specific heat and
electronic structure of and -plutonium using dynmical mean
field theory (DMFT). We use the perturbative T-matrix and fluctuating exchange
(T-matrix FLEX) as a quantum impurity solver. We considered two different
physical pictures of plutonoium. In the first, , the perturbative
treatment of electronic correlations has been carried out around the
non-magnetic (LDA) Hamiltonian, which results in an f occupation around a bit
above . In the second, , plutonium is viewed as being close
to an configuration, and perturbation theory is carried out around the
(LDA+U) starting point bit below . In the latter case the electronic
specific heat coefficient attains a smaller value in -Pu than
in -Pu, in contradiction to experiment, while in the former case our
calculations reproduce the experimentally observed large increase of
in -Pu as compared to the phase. This enhancement of the
electronic specific heat coefficient in -Pu is due to strong electronic
correlations present in this phase, which cause a substantial increase of the
electronic effective mass, and high density of states at . The densities
of states of and -plutonium obtained starting from the
open-shell configuration are also in good agreement with the experimental
photoemission spectra.Comment: 6 pages, 3 figure
Solvent Driven Formation of Bolaamphiphilic Vesicles
We show that a spontaneous bending of single layer bolaamphiphiles results
from the frustration due to the competition between core-core and tail-solvent
interactions. We find that spherical vesicles are stable under rather general
assumptions on these interactions described within the Flory-Huggins theory. We
consider also the deformation of the vesicles in an external magnetic field
that has been recently experimentally observed.Comment: J. Phys. Chem. B, accepte
Friedel oscillations at the surfaces of rhombohedral -layer graphene
The low-energy physics of rhombohedral -layer graphene mainly arises on
the external layers, where most of the {\pi} electrons are located. Their Bloch
band structure defines a two-band semimetal; the dispersion relation scales as
with the momentum norm in the vicinity of two nonequivalent
valleys. In this paper, we address the problem of elastic scattering through a
localized impurity located either on the surface of the material or within the
bulk, and focus on the quantum interferences it induces on the two external
layers. It is apprehended in the framework of a -matrix approach, both
numerically and analytically, regardless of the impurity magnitude, which
enables the description of realistic scatters. In rhombohedral multilayer
graphene, the impurity induces Friedel oscillations that always decay as .
As a result, monolayer graphene is the only material of the rhombohedral class
that exhibits -decaying Friedel oscillations. The interference
patterns are subsequently analyzed in momentum space. This analysis enables a
clear distinction between monolayer graphene and multilayer graphene. It also
shows that the interference pattern reveals the whole Bloch band structure, and
highlights the number of layers stacked in the material, as well as the
-quantized Berry phases that characterize the existence of nodal points
in the semimetallic spectrum. Experimentally, these features may be probed from
scanning tunneling microscopy, when imaging the local density of states at the
surfaces of suspended rhombohedral -layer graphene
Effect of a single impurity on the local density of states in monolayer and bilayer graphene
We use the T-matrix approximation to analyze the effect of a localized
impurity on the local density of states in mono- and bilayer graphene. For
monolayer graphene the Friedel oscillations generated by intranodal scattering
obey an inverse-square law, while the internodal ones obey an inverse law. In
the Fourier transform this translates into a filled circle of high intensity in
the center of the Brillouin zone, and empty circular contours around its
corners. For bilayer graphene both types of oscillations obey an inverse law.Comment: 8 pages, 3 figures, version accepted for publicatio
Magnetism and interaction-induced gap opening in graphene with vacancies or hydrogen adatoms: Quantum Monte Carlo study
We study electronic properties of graphene with finite concentration of
vacancies or other resonant scatterers by a straightforward lattice Quantum
Monte Carlo calculations. Taking into account realistic long-range Coulomb
interaction we calculate distribution of spin density associated to midgap
states and demonstrate antiferromagnetic ordering. Energy gaps are open due to
the interaction effects, both in the bare graphene spectrum and in the
vacancy/impurity bands. In the case of 5 % concentration of resonant scatterers
the latter gap is estimated as 0.7 eV and 1.1 eV for graphene on boron nitride
and freely suspended graphene, respectively.Comment: Text is substantially updated, temperature dependence of order
parameter is added. Accepted for publication in PR
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