6,869 research outputs found
Sputtered Energy Coefficient and Sputtering Yield
This report gives an overview of available calculated sputtered energy coeffi-cients of energetic ions bombarding elemental targets. The energy and angular dependences of the sputtered energy coefficient are fitted by simple formulae for a large number of elemental targets and light (hydrogen and helium) and heavy (mainly noble gases and selfbombardment) bombarding atoms. The incident energies cover a range from 10 to 105 eV, in some cases up to MeV energies. 1
The Latest Red River Rivalry: The Supreme Court\u27s Recent Decision Regarding the Red River Compact
On June 13, 2013, the United States Supreme Court issued a unanimous decision in a “Red River Rivalry” with much greater implications than the annual football game. In Tarrant Regional Water District v. Herrmann, the court sided entirely with Oklahoma in that state’s dispute with Texas over the allocation of Red River water. This decision will have considerable impact on Texas’ ability to meet its ever-growing water needs. Moreover, the decision could be consequential for other interstate water compacts and the states relying on the rivers and tributaries governed by those agreements
Nonequilibrium dynamical mean-field calculations based on the non-crossing approximation and its generalizations
We solve the impurity problem which arises within nonequilibrium dynamical
mean-field theory for the Hubbard model by means of a self-consistent
perturbation expansion around the atomic limit. While the lowest order, known
as the non-crossing approximation (NCA), is reliable only when the interaction
U is much larger than the bandwidth, low-order corrections to the NCA turn out
to be sufficient to reproduce numerically exact Monte Carlo results in a wide
parameter range that covers the insulating phase and the metal-insulator
crossover regime at not too low temperatures. As an application of the
perturbative strong-coupling impurity solver we investigate the response of the
double occupancy in the Mott insulating phase of the Hubbard model to a
dynamical change of the interaction or the hopping, a technique which has been
used as a probe of the Mott insulating state in ultracold fermionic gases.Comment: 14 pages, 9 figure
Measuring correlated electron dynamics with time-resolved photoemission spectroscopy
Time-resolved photoemission experiments can reveal fascinating quantum
dynamics of correlated electrons. However, the thermalization of the electronic
system is typically so fast that very short probe pulses are necessary to
resolve the time evolution of the quantum state, and this leads to poor energy
resolution due to the energy-time uncertainty relation. Although the
photoemission intensity can be calculated from the nonequilibrium electronic
Green functions, the converse procedure is therefore difficult. We analyze a
hypothetical time-resolved photoemission experiment on a correlated electronic
system, described by the Falicov-Kimball model in dynamical mean-field theory,
which relaxes between metallic and insulating phases. We find that the
real-time Green function which describes the transient behavior during the
buildup of the metallic state cannot be determined directly from the
photoemission signal. On the other hand, the characteristic
collapse-and-revival oscillations of an excited Mott insulator can be observed
as oscillating weight in the center of the Mott gap in the time-dependent
photoemission spectrum.Comment: 12 pages, 5 figure
Crossover from adiabatic to sudden interaction quenches in the Hubbard model: Prethermalization and nonequilibrium dynamics
The recent experimental implementation of condensed matter models in optical
lattices has motivated research on their nonequilibrium behavior. Predictions
on the dynamics of superconductors following a sudden quench of the pairing
interaction have been made based on the effective BCS Hamiltonian; however,
their experimental verification requires the preparation of a suitable excited
state of the Hubbard model along a twofold constraint: (i) a sufficiently
nonadiabatic ramping scheme is essential to excite the nonequilibrium dynamics,
and (ii) overheating beyond the critical temperature of superconductivity must
be avoided. For commonly discussed interaction ramps there is no clear
separation of the corresponding energy scales. Here we show that the matching
of both conditions is simplified by the intrinsic relaxation behavior of
ultracold fermionic systems: For the particular example of a linear ramp we
examine the transient regime of prethermalization [M. Moeckel and S. Kehrein,
Phys. Rev. Lett. 100, 175702 (2008)] under the crossover from sudden to
adiabatic switching using Keldysh perturbation theory. A real-time analysis of
the momentum distribution exhibits a temporal separation of an early energy
relaxation and its later thermalization by scattering events. For long but
finite ramping times this separation can be large. In the prethermalization
regime the momentum distribution resembles a zero temperature Fermi liquid as
the energy inserted by the ramp remains located in high energy modes. Thus
ultracold fermions prove robust to heating which simplifies the observation of
nonequilibrium BCS dynamics in optical lattices.Comment: 27 pages, 8 figures Second version with small modifications in
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