89 research outputs found
Localized states due to expulsion of resonant impurity levels from the continuum in bilayer graphene
Anderson impurity problem is considered for a graphene bilayer subject to a
gap-opening bias. In-gap localized states are produced even when the impurity
level overlaps with the continuum of band electrons. The effect depends
strongly on the polarity of the applied bias as long as hybridization with the
impurity occurs within a single layer. For an impurity level inside the
conduction band a positive bias creates the new localized in-gap state. A
negative bias does not produce the same result and leads to a simple broadening
of the impurity level. The implications for transport are discussed including a
possibility of gate-controlled Kondo effect.Comment: 5 pages, 2 figure
The photon absorption edge in superconductors and gapped 1D systems
Opening of a gap in the low-energy excitations spectrum affects the power-law
singularity in the photon absorption spectrum . In the normal state,
the singularity, , is
characterized by an interaction-dependent exponent . On the contrary,
in the supeconducting state the divergence, , is
interaction-independent, while threshold is shifted, ; the ``normal-metal'' form of resumes
at . If the core
hole is magnetic, it creates in-gap states; these states transform drastically
the absorption edge. In addition, processes of scattering off the magnetic core
hole involving spin-flip give rise to inelastic absorption with one or several
{\it real} excited pairs in the final state, yielding a structure of peaks in
at multiples of above the threshold frequency. The above
conclusions apply to a broad class of systems, e.g., Mott insulators, where a
gap opens at the Fermi level due to the interactions.Comment: 6 pages, 5 figures; published versio
A simple microscopic description of quantum Hall transition without Landau levels
By restricting the motion of high-mobility 2D electron gas to a network of
channels with smooth confinement, we were able to trace, both classically and
quantum-mechanically, the interplay of backscattering, and of the bending
action of a weak magnetic field. Backscattering limits the mobility, while
bending initiates quantization of the Hall conductivity. We demonstrate that,
in restricted geometry, electron motion reduces to two Chalker-Coddington
networks, with opposite directions of propagation along the links, which are
weakly coupled by disorder. Interplay of backscattering and bending results in
the quantum Hall transition in a non-quantizing magnetic field, which decreases
with increasing mobility. This is in accord with scenario of floating up
delocalized states.Comment: Published versio
Perturbation theory in radial quantization approach and the expectation values of exponential fields in sine-Gordon model
A perturbation theory for Massive Thirring Model (MTM) in radial quantization
approach is developed. Investigation of the twisted sector in this theory
allows us to calculate the vacuum expectation values of exponential fields of the sine-Gordon theory in first order over Massive Thirring
Models coupling constant. It appears that the apparent difficulty in radial
quantization of massive theories, namely the explicite ''time'' dependence of
the Hamiltonian, may be successfully overcome. The result we have obtained
agrees with the exact formula conjectured by Lukyanov and Zamolodchikov and
coincides with the analogous calculations recently carried out in dual angular
quantization approach by one of the authors.Comment: 16 pages, no figures, LaTe
Fluctuation-enhanced gas sensing
AbstractThe sensitivity of gas sensors was earlier measured by classical method-comparison the resistance of sensors in gas media and air. Here we reported results of the study of low-frequency noise characteristics of sensors. We compare data for different Figaro TGS sensors as well as our sol-gel H2 tin dioxide and porous silicon sensors. The study was performed in dry air and in a mix of dry air with carbon monoxide, hydrogen and alcohol of different concentrations. Higher sensitivity of spectral dependence of noise (SDN) to gas concentration in comparison with classical method of the measurements of gas sensing by a change in the Ohmic resistance part of current-voltage characteristics of samples allows using such SND powerful method for determination of gas concentration in the air or environment
The system of EAS time analysis
The extensive air showers' (EAS) front shape, angle of incidence, disk thickness, particle distribution along the shower, on the delayed and EAS front advancing particles were determined. The suggested system of the EAS time analysis allows determination of the whole EAS longitudinal structure at the observation points. The information from the detectors is continuously recorded in the memory with the memory cell switching in 5 ns, this enables fixation of the moment of pulse input from the detector with an accuracy to + or - 2.5 ns. Along with the fast memory, a slow memory with the cell switching in 1 micron s is introduced in the system, this permits observation of relatively large time intervals with respect to the trigger pulse with an appropriately lower accuracy
Nanoscale Nonlinear Spectroscopy with Electron Beams
We theoretically demonstrate the ability of electron beams to probe the nonlinear photonic response with nanometer spatial resolution, well beyond the capabilities of existing optical techniques. Although the interaction of electron beams with photonic modes is generally weak, the use of optical pumping produces stimulated electronâlight interactions that can exceed order-unity probabilities in photon-induded near field electron microscopy (PINEM). Here, we demonstrate that PINEM can locally and quantitatively probe the nonlinear optical response. Specifically, we predict a dependence of PINEM electron spectra on the sample nonlinearity that can reveal the second-harmonic (SH) response of optical materials with nanometer resolution, observed through asymmetries between electron energy losses and gains. We illustrate this concept by showing that PINEM spectra are sensitive to the SH near field of centrosymmetric structures and by finding substantial spectral asymmetries in geometries for which the linear interaction is reduced
Disorder-induced tail states in a gapped bilayer graphene
The instanton approach to the in-gap fluctuation states is applied to the
spectrum of biased bilayer graphene. It is shown that the density of states
falls off with energy measured from the band-edge as , where the characteristic tail energy,
, scales with the concentration of impurities, , as
. While the bare energy spectrum is characterized by two energies:
the bias-induced gap, , and interlayer tunneling, , the tail,
, contains a {\it single} combination . We
show that the above expression for in the tail actually applies
all the way down to the mid-gap.Comment: 7 pages, 4 figure
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