8,875 research outputs found
Tunable dynamical channel blockade in double-dot Aharonov-Bohm interferometers
We study electronic transport through an Aharonov-Bohm interferometer with
single-level quantum dots embedded in the two arms. The full counting
statistics in the shot-noise regime is calculated to first order in the
tunnel-coupling strength. The interplay of interference and charging energy in
the dots leads to a dynamical channel blockade that is tunable by the magnetic
flux penetrating the Aharonov-Bohm ring. We find super-Poissonian behavior with
diverging second and higher cumulants when the Aharonov-Bohm flux approaches an
integer multiple of the flux quantum.Comment: published version, 10 pages, 10 figure
Full Counting Statistics in Strongly Interacting Systems: Non-Markovian Effects
We present a theory of full counting statistics for electron transport
through interacting electron systems with non-Markovian dynamics. We illustrate
our approach for transport through a single-level quantum dot and a metallic
single-electron transistor to second order in the tunnel-coupling strength, and
discuss under which circumstances non-Markovian effects appear in the transport
properties.Comment: 4 pages, 2 figures, LaTeX; typos added, references adde
Collective Molecular Dynamics in Proteins and Membranes
The understanding of dynamics and functioning of biological membranes and in
particular of membrane embedded proteins is one of the most fundamental
problems and challenges in modern biology and biophysics. In particular the
impact of membrane composition and properties and of structure and dynamics of
the surrounding hydration water on protein function is an upcoming hot topic,
which can be addressed by modern experimental and computational techniques.
Correlated molecular motions might play a crucial role for the understanding
of, for instance, transport processes and elastic properties, and might be
relevant for protein function. Experimentally that involves determining
dispersion relations for the different molecular components, i.e., the length
scale dependent excitation frequencies and relaxation rates. Only very few
experimental techniques can access dynamical properties in biological materials
on the nanometer scale, and resolve dynamics of lipid molecules, hydration
water molecules and proteins and the interaction between them. In this context,
inelastic neutron scattering turned out to be a very powerful tool to study
dynamics and interactions in biomolecular materials up to relevant nanosecond
time scales and down to the nanometer length scale. We review and discuss
inelastic neutron scattering experiments to study membrane elasticity and
protein-protein interactions of membrane embedded proteins
Cotunneling through quantum dots coupled to magnetic leads: zero-bias anomaly for non-collinear magnetic configurations
Cotunneling transport through quantum dots weakly coupled to non-collinearly
magnetized leads is analyzed theoretically by means of the real-time
diagrammatic technique. The electric current, dot occupations, and dot spin are
calculated in the Coulomb blockade regime and for arbitrary magnetic
configuration of the system. It is shown that an effective exchange field
exerted on the dot by ferromagnetic leads can significantly modify the
transport characteristics in non-collinear magnetic configurations, in
particular the zero-bias anomaly found recently for antiparallel configuration.
For asymmetric Anderson model, the exchange field gives rise to precession of
the dot spin, which leads to a nonmonotonic dependence of the differential
conductance and tunnel magnetoresistance on the angle between magnetic moments
of the leads. An enhanced differential conductance and negative TMR are found
for certain non-collinear configurations.Comment: 12 pages, 9 figgure
Efficient few-body calculations in finite volume
Simulating quantum systems in a finite volume is a powerful theoretical tool
to extract information about them. Real-world properties of the system are
encoded in how its discrete energy levels change with the size of the volume.
This approach is relevant not only for nuclear physics, where lattice methods
for few- and many-nucleon states complement phenomenological shell-model
descriptions and ab initio calculations of atomic nuclei based on harmonic
oscillator expansions, but also for other fields such as simulations of cold
atomic systems. This contribution presents recent progress concerning
finite-volume simulations of few-body systems. In particular, it discusses
details regarding the efficient numerical implementation of separable
interactions and it presents eigenvector continuation as a method for
performing robust and efficient volume extrapolations.Comment: 9 pages, 2 figures, ISS 2022 contributio
Deep ALMA imaging of the merger NGC1614 - Is CO tracing a massive inflow of non-starforming gas?
Observations of the molecular gas over scales of 0.5 to several kpc provide
crucial information on how gas moves through galaxies, especially in mergers
and interacting systems, where it ultimately reaches the galaxy center,
accumulates, and feeds nuclear activity. Studying the processes involved in the
gas transport is an important step forward to understand galaxy evolution.
12CO, 13CO and C18O1-0 high-sensitivity ALMA observations were used to assess
properties of the large-scale molecular gas reservoir and its connection to the
circumnuclear molecular ring in NGC1614. The role of excitation and abundances
were studied in this context. Spatial distributions of the 12CO and 13CO
emission show significant differences. 12CO traces the large-scale molecular
gas reservoir, associated with a dust lane that harbors infalling gas. 13CO
emission is - for the first time - detected in the large-scale dust lane. Its
emission peaks between dust lane and circumnuclear molecular ring. A
12CO-to-13CO1-0 intensity ratio map shows high values in the ring region (~30)
typical for the centers of luminous galaxy mergers and even more extreme values
in the dust lane (>45). This drop in ratio is consistent with molecular gas in
the dust lane being in a diffuse, unbound state while being funneled towards
the nucleus. We find a high 16O-to-18O abundance ratio in the starburst region
(>900), typical of quiescent disk gas - by now, the starburst is expected to
have enriched the nuclear ISM in 18O relative to 16O. The massive inflow of gas
may be partially responsible for the low 18O/16O abundance since it will dilute
the starburst enrichment with unprocessed gas from greater radii. The
12CO-to-13CO abundance is consistent with this scenario. It suggests that the
nucleus of NGC1614 is in a transient phase of evolution where starburst and
nuclear growth are fuelled by returning gas from the minor merger event.Comment: 10 pages, 9 figures, accepted for publication in A&
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