5,844 research outputs found
Electron-phonon bound states in graphene in a perpendicular magnetic field
The spectrum of electron-phonon complexes in a monolayer graphene is
investigated in the presence of a perpendicular quantizing magnetic field.
Despite the small electron-phonon coupling, usual perturbation theory is
inapplicable for calculation of the scattering amplitude near the threshold of
the optical phonon emission. Our findings beyond perturbation theory show that
the true spectrum near the phonon emission threshold is completely governed by
new branches, corresponding to bound states of an electron and an optical
phonon with a binding energy of the order of where
is the electron-phonon coupling and the phonon energy.Comment: To be published in Phys. Rev. Lett., 5 pages, 3 figures, 1 tabl
Acoustoelectric current and pumping in a ballistic quantum point contact
The acoustoelectric current induced by a surface acoustic wave (SAW) in a
ballistic quantum point contact is considered using a quantum approach. We find
that the current is of the "pumping" type and is not related to drag, i.e. to
the momentum transfer from the wave to the electron gas. At gate voltages
corresponding to the plateaus of the quantized conductance the current is
small. It is peaked at the conductance step voltages. The peak current
oscillates and decays with increasing SAW wavenumber for short wavelengths.
These results contradict previous calculations, based on the classical
Boltzmann equation.Comment: 4 pages, 1 figur
Quantum dot dephasing by edge states
We calculate the dephasing rate of an electron state in a pinched quantum
dot, due to Coulomb interactions between the electron in the dot and electrons
in a nearby voltage biased ballistic nanostructure. The dephasing is caused by
nonequilibrium time fluctuations of the electron density in the nanostructure,
which create random electric fields in the dot. As a result, the electron level
in the dot fluctuates in time, and the coherent part of the resonant
transmission through the dot is suppressed
Effect of Interactions on the Admittance of Ballistic Wires
A self-consistent theory of the admittance of a perfect ballistic, locally
charge neutral wire is proposed. Compared to a non-interacting theory,
screening effects drastically change the frequency behavior of the conductance.
In the single-channel case the frequency dependence of the admittance is
monotonic, while for two or more channels collective interchannel excitations
lead to resonant structures in the admittance. The imaginary part of the
admittance is typically positive, but can become negative near resonances.Comment: Presentation considerably modified; the results are unchanged. 4
pages, 2 figures .eps-format include
Calorimetry of gamma-ray bursts: echos in gravitational waves
Black holes surrounded by a disk or torus may drive the enigmatic
cosmological gamma-ray bursts (GRBs). Equivalence in poloidal topology to
pulsar magnetospheres shows a high incidence of the black hole-luminosity
into the surrounding magnetized matter. We argue that this emission is
re-radiated into gravitational waves at in frequencies of
order 1kHz, winds and, potentially, MeV neutrinos. The total energy budget and
input to the GRB from baryon poor jets are expected to be standard in this
scenario, consistent with recent analysis of afterglow data. Collimation of
these outflows by baryon rich disk or torus winds may account for the observed
spread in opening angles up to about . This model may be tested by future
LIGO/VIRGO observations.Comment: To appear in ApJ
Induced scattering of short radio pulses
Effect of the induced Compton and Raman scattering on short, bright radio
pulses is investigated. It is shown that when a single pulse propagates through
the scattering medium, the effective optical depth is determined by the
duration of the pulse but not by the scale of the medium. The induced
scattering could hinder propagation of the radio pulse only if close enough to
the source a dense enough plasma is presented. The induced scattering within
the relativistically moving source places lower limits on the Lorentz factor of
the source. The results are applied to the recently discovered short
extragalactic radio pulse.Comment: submitted to Ap
Acoustoelectric effect in a finite-length ballistic quantum channel
The dc current induced by a coherent surface acoustic wave (SAW) of wave
vector q in a ballistic channel of length L is calculated. The current contains
two contributions, even and odd in q. The even current exists only in a
asymmetric channel, when the electron reflection coefficients r_1 and r_2 at
both channel ends are different. The direction of the even current does not
depend on the direction of the SAW propagation, but is reversed upon
interchanging r_1 and r_2. The direction of the odd current is correlated with
the direction of the SAW propagation, but is insensitive to the interchange of
r_1 and r_2. It is shown that both contributions to the current are non zero
only when the electron reflection coefficients at the channel ends are energy
dependent. The current exhibits geometric oscillations as function of qL. These
oscillations are the hallmark of the coherence of the SAW and are completely
washed out when the current is induced by a flux of non-coherent phonons. The
results are compared with those obtained previously by different methods and
under different assumptions.Comment: 7 pages, 2 figure
Classical properties of low-dimensional conductors: Giant capacitance and non-Ohmic potential drop
Electrical field arising around an inhomogeneous conductor when an electrical
current passes through it is not screened, as distinct from 3D conductors, in
low-dimensional conductors. As a result, the electrical field depends on the
global distribution of the conductivity sigma(x) rather than on the local value
of it, inhomogeneities of sigma(x) produce giant capacitances C(omega) that
show frequency dependence at relatively low omega, and electrical fields
develop in vast regions around the inhomogeneities of sigma(x). A theory of
these phenomena is presented for 2D conductors.Comment: 5 pages, two-column REVTeX, to be published in Physical Review
Letter
Anomalous Thermal Transport in Quantum Wires
We study thermal transport in a one-dimensional quantum wire, connected to
reservoirs. Despite of the absence of electron backscattering, interactions in
the wire strongly influence thermal transport. Electrons propagate with unitary
transmission through the wire and electric conductance is not affected. Energy,
however, is carried by bosonic excitations (plasmons) which suffer from
scattering even on scales much larger than the Fermi wavelength. If the
electron density varies randomly, plasmons are localized and {\em charge-energy
separation} occurs. We also discuss the effect of plasmon-plasmon interaction
using Levinson's theory of nonlocal heat transport.Comment: replaced with published versio
- …