1,676 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
Unconventional Hall effect in pnictides from interband interactions
We calculate the Hall transport in a multiband systems with a dominant
interband interaction between carriers having electron and hole character. We
show that this situation gives rise to an unconventional scenario, beyond the
Boltzmann theory, where the quasiparticle currents dressed by vertex
corrections acquire the character of the majority carriers. This leads to a
larger (positive or negative) Hall coefficient than what expected on the basis
of the carrier balance, with a marked temperature dependence. Our results
explain the puzzling measurements in pnictides and they provide a more general
framework for transport properties in multiband materials.Comment: 5 pages, 2 figure
Spin-Hall Conductivity in Electron-Phonon Coupled Systems
We derive the ac spin-Hall conductivity of
two-dimensional spin-orbit coupled systems interacting with dispersionless
phonons of frequency . For the linear Rashba model we show that the
electron-phonon contribution to the spin-vertex corrections breaks the
universality of at low-frequencies and provides a
non-trivial renormalization of the interband resonance. On the contrary, in a
generalized Rashba model for which the spin-vertex contributions are absent,
the coupling to the phonons enters only through the self-energy, leaving the
low frequency behavior of unaffected by the
electron-phonon interaction.Comment: 4 pages, 3 figures, version as printe
Electrical Resistivity of a Thin Metallic Film
The electrical resistivity of a pure sample of a thin metallic film is found
to depend on the boundary conditions. This conclusion is supported by a
free-electron model calculation and confirmed by an ab initio relativistic
Korringa-Kohn-Rostoker computation. The low-temperature resistivity is found to
be zero for a free-standing film (reflecting boundary conditions) but nonzero
when the film is sandwiched between two semi-infinite samples of the same
material (outgoing boundary conditions). In the latter case, this resistivity
scales inversely with the number of monolayers and is due to the background
diffusive scattering by a finite lattice.Comment: 20 pages. To be published in Physical Review B, December 15, 199
Phase diagram for Coulomb-frustrated phase separation in systems with negative short-range compressibility
Using numerical techniques and asymptotic expansions we obtain the phase
diagram of a paradigmatic model of Coulomb frustrated phase separation in
systems with negative short-range compressibility. The transition from the
homogeneous phase to the inhomogeneous phase is generically first order in
isotropic three-dimensional systems except for a critical point. Close to the
critical point, inhomogeneities are predicted to form a BCC lattice with
subsequent transitions to a triangular lattice of rods and a layered structure.
Inclusion of a strong anisotropy allows for second- and first-order transition
lines joined by a tricritical point.Comment: 4 pages, 3 figures. Improved figures and presentatio
Vanishing conductivity of quantum solitons in polyacetylene
Quantum solitons or polarons are supposed to play a crucial role in the
electric conductivity of polyacetylene, in the intermediate doping regime. We
present an exact fully quantized calculation of the quantum soliton
conductivity in polyacetylene and show that it vanishes exactly. This is
obtained by applying a general method of soliton quantization, based on
order-disorder duality, to a Z(2)-symmetric complex extension of the TLM
dimerization effective field theory. We show that, in this theory,
polyacetylene solitons are sine-Gordon solitons in the phase of the complex
field.Comment: To appear in J. Phys. A: Math. Theor., 15 page
One Dimensional Gas of Bosons with Feshbach Resonant Interactions
We present a study of a gas of bosons confined in one dimension with Feshbach
resonant interactions, at zero temperature. Unlike the gas of one dimensional
bosons with non-resonant interactions, which is known to be equivalent to a
system of interacting spinless fermions and can be described using the
Luttinger liquid formalism, the resonant gas possesses novel features.
Depending on its parameters, the gas can be in one of three possible regimes.
In the simplest of those, it can still be described by the Luttinger liquid
theory, but its Fermi momentum cannot be larger than a certain cutoff momentum
dependent on the details of the interactions. In the other two regimes, it is
equivalent to a Luttinger liquid at low density only. At higher densities its
excitation spectrum develops a minimum, similar to the roton minimum in helium,
at momenta where the excitations are in resonance with the Fermi sea. As the
density of the gas is increased further, the minimum dips below the Fermi
energy, thus making the ground state unstable. At this point the standard
ground state gets replaced by a more complicated one, where not only the states
with momentum below the Fermi points, but also the ones with momentum close to
that minimum, get filled, and the excitation spectrum develops several
branches. We are unable so far to study this new regime in detail due to the
lack of the appropriate formalism.Comment: 20 pages, 18 figure
Nonlinear c-axis transport in Bi_2Sr_2CaCu_2O_(8+d) from two-barrier tunneling
Motivated by the peculiar features observed through intrinsic tunneling
spectroscopy of BiSrCaCuO mesas in the normal state,
we have extended the normal state two-barrier model for the c-axis transport
[M. Giura et al., Phys. Rev. B {\bf 68}, 134505 (2003)] to the analysis of
curves. We have found that the purely normal-state model reproduces all
the following experimental features: (a) the parabolic -dependence of
in the high- region (above the conventional pseudogap temperature),
(b) the emergence and the nearly voltage-independent position of the "humps"
from this parabolic behavior lowering the temperature, and (c) the crossing of
the absolute curves at a characteristic voltage . Our
findings indicate that conventional tunneling can be at the origin of most of
the uncommon features of the c axis transport in
BiSrCaCuO. We have compared our calculations to
experimental data taken in severely underdoped and slightly underdoped
BiSrCaCuO small mesas. We have found good agreement
between the data and the calculations, without any shift of the calculated
dI/dV on the vertical scale. In particular, in the normal state (above
) simple tunneling reproduces the experimental dI/dV quantitatively.
Below quantitative discrepancies are limited to a simple rescaling of
the voltage in the theoretical curves by a factor 2. The need for such
modifications remains an open question, that might be connected to a change of
the charge of a fraction of the carriers across the pseudogap opening.Comment: 7 pages, 5 figure
Theory of the high-frequency chiral optical response in a p_x+ip_y superconductor
The optical Hall conductivity and the polar Kerr angle are calculated as
functions of temperature for a two-dimensional chiral p_x+ip_y superconductor,
where the time-reversal symmetry is spontaneously broken. The theoretical
estimate for the polar Kerr angle agrees by the order of magnitude with the
recent experimental measurement in Sr2RuO4 by Xia et al. cond-mat/0607539. The
theory predicts that the Kerr angle is proportional to the square of the
superconducting energy gap and is inversely proportional to the cube of
frequency, which can be verified experimentally.Comment: 4 pages, no figures, RevTeX. V.2: one reference and discussion of
horizontal lines of nodes added. V.3: a typo corrected, and one reference
added. V.4: two references added and minor stylistic changes made, as in the
published versio
Theory of Polaron Resonance in Quantum Dots and Quantum-Dot Molecules
The theory of exciton coupling to photons and LO phonons in quantum dots
(QDs) and quantum-dot molecules (QDMs) is presented. Resonant-round trips of
the exciton between the ground (bright) and excited (dark or bright) states
mediated by the LO-phonon alter the decay time and yield the Rabi oscillation.
The initial distributions of the population in the ground and the excited
states dominate the oscillating amplitude and frequency. This property provides
a detectable signature to the information stored in a qubit made from QD or QDM
for a wide range of temperature T. Our results presented herein provide an
explanation to the anomaly on T-dependent decay in self-assembled InGaAs/GaAs
QDMs recently reported by experiment.Comment: 30 pages, 8 figure
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