2,486 research outputs found
Theory of Polar Corrections to Donor Binding
We calculate the optical phonon correction to the binding energy of electrons
to donors in cubic materials. Previous theories calculated the Rydberg energy
reduced by the effective mass and the static dielectric function. They omitted
an important energy term from the long-range polarization of the ionized donor,
which vanishes for the neutral donor. They also omitted the donor-phonon
interaction. Including these terms yields a new formula for the donor binding
energy
Electron-phonon heat transfer in monolayer and bilayer graphene
We calculate the heat transfer between electrons to acoustic and optical
phonons in monolayer and bilayer graphene (MLG and BLG) within the
quasiequilibrium approximation. For acoustic phonons, we show how the
temperature-power laws of the electron-phonon heat current for BLG differ from
those previously derived for MLG and note that the high-temperature
(neutral-regime) power laws for MLG and BLG are also different, with a weaker
dependence on the electronic temperature in the latter. In the general case we
evaluate the heat current numerically. We suggest that a measurement of the
heat current could be used for an experimental determination of the
electron-acoustic phonon coupling constants, which are not accurately known.
However, in a typical experiment heat dissipation by electrons at very low
temperatures is dominated by diffusion, and we estimate the crossover
temperature at which acoustic-phonon coupling takes over in a sample with Joule
heating. At even higher temperatures optical phonons begin to dominate. We
study some examples of potentially relevant types of optical modes, including
in particular the intrinsic in-plane modes, and additionally the remote surface
phonons of a possible dielectric substrate.Comment: 13 pages, 8 figures; moved details to appendixes, added discussion of
remote phonon
Multiple Particle Scattering in Quantum Point Contacts
Recent experiments performed on weakly pinched quantum point contacts, have
shown a resistance that tend to decrease at low source drain voltage. We show
that enhanced Coulomb interactions, prompt by the presence of the point
contact, may lead to anomalously large multiple-particle scattering at finite
bias voltage. These processes tend to decrease at low voltage, and thus may
account for the observed reduction of the resistance. We concentrate on the
case of a normal point contact, and model it by a spinfull interacting
Tomonaga-Luttinger liquid, with a single impurity, connected to non interacting
leads. We find that sufficiently strong Coulomb interactions enhance
two-electron scattering, so as these dominate the conductance. Our calculation
shows that the effective charge, probed by the shot noise of such a system,
approaches a value proportional to e* = 2e at sufficiently large backscattering
current. This distinctive hallmark may be tested experimentally. We discuss
possible applications of this model to experiments conducted on Hall bars.Comment: 5 pages, 2 figure
Spectroscopy for cold atom gases in periodically phase-modulated optical lattices
The response of cold atom gases to small periodic phase modulation of an
optical lattice is discussed. For bosonic gases, the energy absorption rate is
given, within linear response theory, by imaginary part of the current
correlation function. For fermionic gases in a strong lattice potential, the
same correlation function can be probed via the production rate double
occupancy. The phase modulation gives thus direct access to the conductivity of
the system, as function of the modulation frequency. We give an example of
application in the case of one dimensional bosons at zero temperature and
discuss the link between the phase- and amplitude-modulation.Comment: 4 pages, 2 figures, final versio
Analysis of transport properties of iron pnictides: spin-fluctuation scenario
We present a phenomenological theory of quasiparticle scattering and
transport relaxation in the normal state of iron pnictides based on the
simplified two-band model coupled via spin fluctuations. In analogy with
anomalous properties of cuprates it is shown that a large and anomalous
normal-state resistivity and thermopower can be interpreted as the consequence
of strong coupling to spin fluctuations. The generalization to the
superconducting phase is also discussed.Comment: Revised version, 6 pages, 11 references adde
Friedel oscillations in disordered quantum wires: Influence of e-e interactions on the localization length
The Friedel oscillations caused due to an impurity located at one edge of a
disordered interacting quantum wire are calculated numerically. The electron
density in the system's ground state is determined using the DMRG method, and
the Friedel oscillations data is extracted using the density difference between
the case in which the wire is coupled to an impurity and the case where the
impurity is uncoupled. We show that the power law decay of the oscillations
occurring for an interacting clean 1D samples described by Luttinger liquid
theory, is multiplied by an exponential decay term due to the disorder. Scaling
of the average Friedel oscillations by this exponential term collapses the
disordered samples data on the clean results. We show that the length scale
governing the exponential decay may be associated with the Anderson
localization length and thus be used as a convenient way to determine the
dependence of the localization length on disorder and interactions. The
localization length decreases as a function of the interaction strength, in
accordance with previous predictions.Comment: 7 pages, 7 figure
Metal-insulator transition caused by the coupling to localized charge-frustrated systems under ice-rule local constraint
We report the results of our theoretical and numerical study on electronic
and transport properties of fermion systems with charge frustration. We
consider an extended Falicov-Kimball model in which itinerant spinless fermions
interact repulsively by U with localized particles whose distribution satisfies
a local constraint under geometrical frustration, the so-called ice rule. We
numerically calculate the density of states, optical conductivity, and inverse
participation ratio for the models on the pyrochlore, checkerboard, and kagome
lattices, and discuss the nature of metal-insulator transitions at commensurate
fillings. As a result, we show that the ice-rule local constraint leads to
several universal features in the electronic structure; a charge gap opens at a
considerably small U compared to the bandwidth, and the energy spectrum
approaches a characteristic form in the large U limit, that is, the
noninteracting tight-binding form in one dimension or the -functional
peak. In the large U region, the itinerant fermions are confined in the
macroscopically-degenerate ice-rule configurations, which consist of a bunch of
one-dimensional loops: We call this insulating state the charge ice. On the
other hand, transport properties are much affected by the geometry and
dimensionality of lattices; e.g., the pyrochlore lattice model exhibits a
transition from a metallic to the charge-ice insulating state by increasing U,
while the checkerboard lattice model appears to show Anderson localization
before opening a gap. Meanwhile, in the kagome lattice case, we do not obtain
clear evidence of Anderson localization. Our results elucidate the universality
and diversity of phase transitions to the charge-ice insulator in fully
frustrated lattices.Comment: 16 pages, 17 figure
Novel theoretical approach in photoemission spectroscopy: application to isotope effect and boron-doped diamond
A new path-integral theory is developed to calculate the photoemission
spectra (PES) of correlated many-electron systems. The application to the study
on Bi2Sr2CaCu2O8 (Bi2212) and boron-doped diamond (BDD) is discussed in
details. It is found that the isotopic shift in the angle-resolved
photoemission spectra of Bi2212 is due to the off-diagonal quadratic
electron-phonon (e-ph) coupling, whereas the presence of electron-electron
repulsion partially suppresses this effect. For the BDD, a semiconductor-metal
phase transition, which is induced by increasing the e-ph coupling and dopant
concentration, is reproduced by our theory. Additionally, the presence of Fermi
edge and phonon step-like structure in PES is found to be due to a co-existence
of itinerant and localized electronic states in BDD.Comment: 6 pages, 4 figures, Procs. of LEHTSC 2007, submitted to J. Phys.:
Conf. Se
Spin-Seebeck effect in a strongly interacting Fermi gas
We study the spin-Seebeck effect in a strongly interacting, two-component
Fermi gas and propose an experiment to measure this effect by relatively
displacing spin up and spin down atomic clouds in a trap using spin-dependent
temperature gradients. We compute the spin-Seebeck coefficient and related
spin-heat transport coefficients as functions of temperature and interaction
strength. We find that when the inter-spin scattering length becomes larger
than the Fermi wavelength, the spin-Seebeck coefficient changes sign as a
function of temperature, and hence so does the direction of the
spin-separation. We compute this zero-crossing temperature as a function of
interaction strength and in particular in the unitary limit for the inter-spin
scattering
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