55 research outputs found
A partial fraction decomposition of the Fermi function
A partial fraction decomposition of the Fermi function resulting in a finite
sum over simple poles is proposed. This allows for efficient calculations
involving the Fermi function in various contexts of electronic structure or
electron transport theories. The proposed decomposition converges in a
well-defined region faster than exponential and is thus superior to the
standard Matsubara expansion.Comment: 7 pages, 5 figure
Full Counting Statistics of a Non-adiabatic Electron Pump
Non-adiabatic charge pumping through a single-level quantum dot with
periodically modulated parameters is studied theoretically. By means of a
quantum-master-equation approach the full counting statistics of the system is
obtained. We find a trinomial-probability distribution of the charge transfer,
which adequately describes the reversal of the pumping current by sweeping the
driving frequency. Further, we derive equations of motion for current and
noise, and solve those numerically for two different driving schemes. Both show
interesting features which can be fully analyzed due to the simple and generic
model studied.Comment: 7 pages, 4 figure
Attosecond resolved charging of clusters
Attosecond laser pulses open the door to resolve microscopic electron
dynamics in time. Experiments performed include the decay of a core hole, the
time-resolved measurement of photo ionization and electron tunneling. The
processes investigated share the coherent character of the dynamics involving
very few, ideally one active electron. Here, we introduce a scheme to probe
dissipative multi-electron motion in time. In this context attosecond probing
enables one to obtain information which is lost at later times and cannot be
retrieved by conventional methods in the energy domain due to the incoherent
nature of the dynamics. As a specific example we will discuss the charging of a
rare-gas cluster during a strong femtosecond pulse with attosecond pulses. The
example illustrates the proposed use of attosecond pulses and suggests an
experimental resolution of a controversy about the mechanism of energy
absorption by rare-gas clusters in strong vacuum-ultraviolet (VUV) pulses.Comment: 4 pages, 3 figure
Energy absorption of xenon clusters in helium nanodroplets under strong laser pulses
Energy absorption of xenon clusters embedded in helium nanodroplets from
strong femtosecond laser pulses is studied theoretically. Compared to pure
clusters we find earlier and more efficient energy absorption in agreement with
experiments. This effect is due to resonant absorption of the helium nanoplasma
whose formation is catalyzed by the xenon core. For very short double pulses
with variable delay both plasma resonances, due to the helium shell and the
xenon core, are identified and the experimental conditions are given which
should allow for a simultaneous observation of both of them.Comment: 4 pages, 4 figure
Floquet approach for dynamics in short and intense laser pulses
We present a two-timescale Floquet method that allows one to apply the
Kramers-Henneberger approach to short pulses and arbitrary laser frequencies.
An efficient numerical procedure to propagate the Floquet Hamiltonian is
provided that relies on the Toeplitz matrix formalism and Fast Fourier
Transformations. It enables efficient time propagation with large Floquet
expansions, while still taking advantage of the cycle-averaged
Kramers-Henneberger basis. Three illustrative cases of ionization with
different photon energies are analyzed, where the envelope of a short and
intense pulse is crucial to the underlying dynamics.Comment: 39 pages, 11 figure
Proton ejection from molecular hydride clusters exposed to strong X-ray pulses
Clusters consisting of small molecules containing hydrogen do eject fast
protons when illuminated by short X-ray pulses. A suitable overall charging of
the cluster controlled by the X-ray intensity induces electron migration from
the surface to the bulk leading to efficient segregation of the protons and to
a globally hindered explosion of the heavy atoms even outside the screened
volume. We investigate this peculiar effect systematically along the
iso-electronic sequence of methane over ammonia and water to the atomic limit
of neon as a reference. In contrast to core-shell systems where the outer shell
is sacrificed to reduce radiation damage, the intricate proton dynamics of
hydride clusters allows one to keep the entire backbone of heavy atoms intact.Comment: 5 pages, 5 figure
Prevailing features of X-ray induced molecular electron spectra revealed with fullerenes
Intense X-ray photo-absorption from short and intense pulses by a molecule
triggers complicated electron and subsequently ion dynamics leading to
photo-electron spectra which are difficult to interpret. Illuminating
fullerenes offers a way to separate out the electron dynamics. Moreover, the
fullerene cage confines spatially the origin of photo and Auger electrons.
Together with the sequential nature of the photo processes at intensities
available at X-ray free electron lasers, this allows for a remarkably detailed
interpretation of the photo-electron spectra as we will demonstrate. The
general features derived can serve as a paradigm for less well-defined
situations in other large molecules or clusters.Comment: 5 pages, 5 figure
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