37,692 research outputs found
Algebraic solution of a graphene layer in a transverse electric and perpendicular magnetic fields
We present an exact algebraic solution of a single graphene plane in
transverse electric and perpendicular magnetic fields. The method presented
gives both the eigen-values and the eigen-functions of the graphene plane. It
is shown that the eigen-states of the problem can be casted in terms of
coherent states, which appears in a natural way from the formalism.Comment: 11 pages, 5 figures, accepted for publication in Journal of Physics
Condensed Matte
Conductivity of suspended and non-suspended graphene at finite gate voltage
We compute the DC and the optical conductivity of graphene for finite values
of the chemical potential by taking into account the effect of disorder, due to
mid-gap states (unitary scatterers) and charged impurities, and the effect of
both optical and acoustic phonons. The disorder due to mid-gap states is
treated in the coherent potential approximation (CPA, a self-consistent
approach based on the Dyson equation), whereas that due to charged impurities
is also treated via the Dyson equation, with the self-energy computed using
second order perturbation theory. The effect of the phonons is also included
via the Dyson equation, with the self energy computed using first order
perturbation theory. The self-energy due to phonons is computed both using the
bare electronic Green's function and the full electronic Green's function,
although we show that the effect of disorder on the phonon-propagator is
negligible. Our results are in qualitative agreement with recent experiments.
Quantitative agreement could be obtained if one assumes water molelcules under
the graphene substrate. We also comment on the electron-hole asymmetry observed
in the DC conductivity of suspended graphene.Comment: 13 pages, 11 figure
Conductance quantization and transport gap in disordered graphene nanoribbons
We study numerically the effects of edge and bulk disorder on the conductance
of graphene nanoribbons. We compute the conductance suppression due to
localization induced by edge scattering. We find that even for weak edge
roughness, conductance steps are suppressed and transport gaps appear. These
gaps are approximately inversely proportional to the nanoribbon width. On/off
conductance ratios grow exponentially with the nanoribbon length. Our results
impose severe limitations to the use of graphene in ballistic nanowires.Comment: 5 pages, 7 figures; references added, typos fixed, to appear in Phys.
Rev
Effects of a mixed vector-scalar kink-like potential for spinless particles in two-dimensional spacetime
The intrinsically relativistic problem of spinless particles subject to a
general mixing of vector and scalar kink-like potentials () is investigated. The problem is mapped into the exactly solvable
Surm-Liouville problem with the Rosen-Morse potential and exact bounded
solutions for particles and antiparticles are found. The behaviour of the
spectrum is discussed in some detail. An apparent paradox concerning the
uncertainty principle is solved by recurring to the concept of effective
Compton wavelength.Comment: 13 pages, 4 figure
Correlation between the transition temperature and the superfluid density in BCS superconductor NbB_2+x
The results of the muon-spin rotation experiments on BCS superconductors
NbB_2+x (x = 0.2, 0.34) are reported. Both samples, studied in the present
work, exhibit rather broad transitions to the superconducting state, suggesting
a distribution of the volume fractions with different transition temperatures
(T_c)'s. By taking these distributions into account, the dependence of the
inverse squared zero-temperature magnetic penetration depth (\lambda_0^{-2}) on
T_c was reconstructed for temperatures in the range 1.5K<T_c<8.0K.
\lambda_0^{-2} was found to obey the power law dependence \lambda_0^{-2}\propto
T_c^{3.1(1)} which appears to be common for some families of BCS
superconductors as, {\it e.g.}, Al doped MgB_2 and high-temperature cuprate
superconductors as underdoped YBa_2Cu_3O_{7-\delta}.Comment: 9 pages, 7 figures. Accepted for publication in Phys. Rev.
Non-linear excitations in 1D correlated insulators
In this work we investigate charge transport in one-dimensional (1D)
insulators via semi-classical and perturbative renormalization group (RG)
methods. We consider the problem of electron-electron, electron-phonon and
electron-two-level system interactions. We show that non-linear collective
modes such as polarons and solitons are reponsible for transport. We find a new
excitation in the Mott insulator: the polaronic soliton. We discuss the
differences between band and Mott insulators in terms of their spin spectrum
and obtain the charge and spin gaps in each one of these systems. We show that
electron-electron interactions provide strong renormalizations of the energy
scales in the problem.Comment: 29 page
Confined magneto-optical waves in graphene
The electromagnetic mode spectrum of single-layer graphene subjected to a
quantizing magnetic field is computed taking into account intraband and
interband contributions to the magneto-optical conductivity. We find that a
sequence of weakly decaying quasi-transverse-electric modes, separated by
magnetoplasmon polariton modes, emerge due to the quantizing magnetic field.
The characteristics of these modes are tuneable, by changing the magnetic field
or the Fermi energy.Comment: 9 pages, 7 figures. published version: text and figures revised and
updated + new references and one figure adde
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