267 research outputs found
Electron relaxation in metals: Theory and exact analytical solutions
The non-equilibrium dynamics of electrons is of a great experimental and
theoretical value providing important microscopic parameters of the Coulomb and
electron-phonon interactions in metals and other cold plasmas. Because of the
mathematical complexity of collision integrals theories of electron relaxation
often rely on the assumption that electrons are in a "quasi-equilibrium" (QE)
with a time-dependent temperature, or on the numerical integration of the
time-dependent Boltzmann equation. We transform the integral Boltzmann equation
to a partial differential Schroedinger-like equation with imaginary time in a
one-dimensional "coordinate" space reciprocal to energy which allows for exact
analytical solutions in both cases of electron-electron and electron-phonon
relaxation. The exact relaxation rates are compared with the QE relaxation
rates at high and low temperatures.Comment: Citation list has been extended. The paper is submitted to the
Physical Review
Entropy Driven Atomic Motion in Laser-Excited Bismuth
We introduce a thermodynamical model based on the two-temperature approach in order to fully understand the dynamics of the coherent A(1g) phonon in laser-excited bismuth. Using this model, we simulate the time evolution of (111) Bragg peak intensities measured by Fritz et al. [Science 315, 633 (2007)] in femtosecond x-ray diffraction experiments performed on a bismuth film for different laser fluences. The agreement between theoretical and experimental results is striking not only because we use fluences very close to the experimental ones but also because most of the model parameters are obtained from ab initio calculations performed for different electron temperatures
Electron-Phonon Coupling in High-Temperature Cuprate Superconductors Determined from Electron Relaxation Rates
We determined electronic relaxation times via pump-probe optical spectroscopy
using sub-15 fs pulses for the normal state of two different cuprate
superconductors.We show that the primary relaxation process is the
electron-phonon interaction and extract a measure of its strength, the second
moment of the Eliashberg function\lambda=800\pm200 meV^{2} for
La_{1.85}Sr_{0.15}CuO_{4} and \lambda=400\pm100 meV^{2} for
YBa_{2}Cu_{3}O_{6.5}. These values suggest a possible fundamental role of the
electron-phonon interaction in the superconducting pairing mechanism.Comment: As published in PR
Evolution of the magnetic phase transition in MnO confined to channel type matrices. Neutron diffraction study
Neutron diffraction studies of antiferromagnetic MnO confined to MCM-41 type
matrices with channel diameters 24-87 A demonstrate a continuous magnetic phase
transition in contrast to a discontinuous first order transition in the bulk.
The character of the magnetic transition transforms with decreasing channel
diameter, showing the decreasing critical exponent and transition temperature,
however the latter turns out to be above the N\'eel temperature for the bulk.
This enhancement is explained within the framework of Landau theory taking into
consideration the ternary interaction of the magnetic and associated structural
order parameters.Comment: 6 pages pdf file, including 4 figures, uses revtex4.cl
The Origin of Anomalous Low-Temperature Downturns in the Thermal Conductivity of Cuprates
We show that the anomalous decrease in the thermal conductivity of cuprates
below 300 mK, as has been observed recently in several cuprate materials
including PrCeCuO in the field-induced normal state,
is due to the thermal decoupling of phonons and electrons in the sample. Upon
lowering the temperature, the phonon-electron heat transfer rate decreases and,
as a result, a heat current bottleneck develops between the phonons, which can
in some cases be primarily responsible for heating the sample, and the
electrons. The contribution that the electrons make to the total low- heat
current is thus limited by the phonon-electron heat transfer rate, and falls
rapidly with decreasing temperature, resulting in the apparent low- downturn
of the thermal conductivity. We obtain the temperature and magnetic field
dependence of the low- thermal conductivity in the presence of
phonon-electron thermal decoupling and find good agreement with the data in
both the normal and superconducting states.Comment: 8 pages, 5 figure
Ab-initio calculation of all-optical time-resolved calorimetry of nanosized systems: Evidence of nanosecond-decoupling of electron and phonon temperatures
The thermal dynamics induced by ultrashort laser pulses in nanoscale systems,
i.e. all-optical time-resolved nanocalorimetry is theoretically investigated
from 300 to 1.5 K. We report ab-initio calculations describing the temperature
dependence of the electron-phonon interactions for Cu nanodisks supported on
Si. The electrons and phonons temperatures are found to decouple on the ns time
scale at 10 K, which is two orders of magnitude in excess with respect to that
found for standard low-temperature transport experiments. By accounting for the
physics behind our results we suggest an alternative route for overhauling the
present knowledge of the electron-phonon decoupling mechanism in nanoscale
systems by replacing the mK temperature requirements of conventional
experiments with experiments in the time-domain.Comment: 5 pages, 3 figures. Accepted on Physical Review B
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