438 research outputs found
Infrared spectroscopy of hole doped ABA-stacked trilayer graphene
Using infrared spectroscopy, we investigate bottom gated ABA-stacked trilayer
graphene subject to an additional environment-induced p-type doping. We find
that the Slonczewski-Weiss-McClure tight-binding model and the Kubo formula
reproduce the gate voltage-modulated reflectivity spectra very accurately. This
allows us to determine the charge densities and the potentials of the
{\pi}-band electrons on all graphene layers separately and to extract the
interlayer permittivity due to higher energy bands.Comment: 6 pages, 6 figures Corrected sign of fig 3 and visibilty of fig
Full Quantum Analysis of Two-Photon Absorption Using Two-Photon Wavefunction: Comparison with One-Photon Absorption
For dissipation-free photon-photon interaction at the single photon level, we
analyze one-photon transition and two-photon transition induced by photon pairs
in three-level atoms using two-photon wavefunctions. We show that the
two-photon absorption can be substantially enhanced by adjusting the time
correlation of photon pairs. We study two typical cases: Gaussian wavefunction
and rectangular wavefunction. In the latter, we find that under special
conditions one-photon transition is completely suppressed while the high
probability of two-photon transition is maintained.Comment: 6 pages, 4 figure
General properties of response functions of nonequilibrium steady states
We derive general properties, which hold for both quantum and classical
systems, of response functions of nonequilibrium steady states. We clarify
differences from those of equilibrium states. In particular, sum rules and
asymptotic behaviors are derived, and their implications are discussed. Since
almost no assumptions are made, our results are applicable to diverse physical
systems. We also demonstrate our results by a molecular dynamics simulation of
a many-body interacting system.Comment: After publication of this paper, several typos were found, which have
been fixed in the erratum (J. Phys. Soc. Jpn., 80 (2011) 128001). All the
corrections have been made in this updated arXive version. 13 pages with 3
figure
Transient Oscillation of Currents in Quantum Hall Effect of Bloch Electrons
We consider the quantum Hall effect of two-dimensional electrons with a
periodic potential and study the time dependence of the Hall and longitudinal
currents when the electric field is applied abruptly. We find that the currents
oscillate in time with very large frequencies because of quantum fluctuation
and the oscillations eventually vanish, for their amplitudes decay as 1/t.Comment: 16 pages and 8 figure
Gate-induced magneto-oscillation phase anomalies in graphene bilayers
The magneto-oscillations in graphene bilayers are studied in the vicinity of
the K and K' points of the Brillouin zone within the four-band continuum model
ased on the simplest tight-binding approximation involving only the nearest
neighbor interactions. The model is employed to construct Landau plots for a
variety of carrier concentrations and bias strengths between the graphene
planes. The quantum-mechanical and quasiclassical approaches are compared. We
found that the quantum magneto-oscillations are only asymptotically periodic
and reach the frequencies predicted quasiclassically for high indices of Landau
levels. In unbiased bilayers the phase of oscillations is equal to the phase of
massive fermions. Anomalous behavior of oscillation phases was found in biased
bilayers with broken inversion symmetry. The oscillation frequencies again tend
to quasiclassically predicted ones, which are the same for and , but
the quantum approach yields the gate-tunable corrections to oscillation phases,
which differ in sign for K and K'. These valley-dependent phase corrections
give rise, instead of a single quasiclassical series of oscillations, to two
series with the same frequency but shifted in phase.Comment: 8 pages, 8 figure
The electronic properties of bilayer graphene
We review the electronic properties of bilayer graphene, beginning with a
description of the tight-binding model of bilayer graphene and the derivation
of the effective Hamiltonian describing massive chiral quasiparticles in two
parabolic bands at low energy. We take into account five tight-binding
parameters of the Slonczewski-Weiss-McClure model of bulk graphite plus intra-
and interlayer asymmetry between atomic sites which induce band gaps in the
low-energy spectrum. The Hartree model of screening and band-gap opening due to
interlayer asymmetry in the presence of external gates is presented. The
tight-binding model is used to describe optical and transport properties
including the integer quantum Hall effect, and we also discuss orbital
magnetism, phonons and the influence of strain on electronic properties. We
conclude with an overview of electronic interaction effects.Comment: review, 31 pages, 15 figure
Phase Transition in a One-Dimensional Extended Peierls-Hubbard Model with a Pulse of Oscillating Electric Field: I. Threshold Behavior in Ionic-to-Neutral Transition
Photoinduced dynamics of charge density and lattice displacements is
calculated by solving the time-dependent Schr\"odinger equation for a
one-dimensional extended Peierls-Hubbard model with alternating potentials for
the mixed-stack organic charge-transfer complex, TTF-CA. A pulse of oscillating
electric field is incorporated into the Peierls phase of the transfer integral.
The frequency, the amplitude, and the duration of the pulse are varied to study
the nonlinear and cooperative character of the photoinduced transition. When
the dimerized ionic phase is photoexcited, the threshold behavior is clearly
observed by plotting the final ionicity as a function of the increment of the
total energy. Above the threshold photoexcitation, the electronic state reaches
the neutral one with equidistant molecules after the electric field is turned
off. The transition is initiated by nucleation of a metastable neutral domain,
for which an electric field with frequency below the linear absorption peak is
more effective than that at the peak. When the pulse is strong and short, the
charge transfer takes place on the same time scale with the disappearance of
dimerization. As the pulse becomes weak and long, the dimerization-induced
polarization is disordered to restore the inversion symmetry on average before
the charge transfer takes place to bring the system neutral. Thus, a
paraelectric ionic phase is transiently realized by a weak electric field. It
is shown that infrared light also induces the ionic-to-neutral transition,
which is characterized by the threshold behavior.Comment: 24 pages, 11 figure
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