3,102 research outputs found
Covalently Binding the Photosystem I to Carbon Nanotubes
We present a chemical route to covalently couple the photosystem I (PS I) to
carbon nanotubes (CNTs). Small linker molecules are used to connect the PS I to
the CNTs. Hybrid systems, consisting of CNTs and the PS I, promise new
photo-induced transport phenomena due to the outstanding optoelectronic
properties of the robust cyanobacteria membrane protein PS I
Addition Spectra of Chaotic Quantum Dots: Interplay between Interactions and Geometry
We investigate the influence of interactions and geometry on ground states of
clean chaotic quantum dots using the self-consistent Hartree-Fock method. We
find two distinct regimes of interaction strength: While capacitive energy
fluctuations follow approximately a random matrix prediction for
weak interactions, there is a crossover to a regime where is
strongly enhanced and scales roughly with interaction strength. This
enhancement is related to the rearrangement of charges into ordered states near
the dot edge. This effect is non-universal depending on dot shape and size. It
may provide additional insight into recent experiments on statistics of Coulomb
blockade peak spacings.Comment: 4 pages, final version to appear in Phys. Rev. Let
Microwave spectroscopy on a double quantum dot with an on-chip Josephson oscillator
We present measurements on microwave spectroscopy on a double quantum dot
with an on-chip microwave source. The quantum dots are realized in the
two-dimensional electron gas of an AlGaAs/GaAs heterostructure and are weakly
coupled in series by a tunnelling barrier forming an 'ionic' molecular state.
We employ a Josephson oscillator formed by a long Nb/Al-AlO/Nb junction as
a microwave source. We find photon-assisted tunnelling sidebands induced by the
Josephson oscillator, and compare the results with those obtained using an
externally operated microwave source.Comment: 6 pages, 4 figure
Quantum Dots with Disorder and Interactions: A Solvable Large-g Limit
We show that problem of interacting electrons in a quantum dot with chaotic
boundary conditions is solvable in the large-g limit, where g is the
dimensionless conductance of the dot. The critical point of the
theory (whose location and exponent are known exactly) that separates strong
and weak-coupling phases also controls a wider fan-shaped region in the
coupling-1/g plane, just as a quantum critical point controls the fan in at
T>0. The weak-coupling phase is governed by the Universal Hamiltonian and the
strong-coupling phase is a disordered version of the Pomeranchuk transition in
a clean Fermi liquid. Predictions are made in the various regimes for the
Coulomb Blockade peak spacing distributions and Fock-space delocalization
(reflected in the quasiparticle width and ground state wavefunction).Comment: 4 pages, 2 figure
Transmission through a n interacting quantum dot in the Coulomb blockade regime
The influence of electron-electron (e-e) interactions on the transmission
through a quantum dot is investigated numerically for the Coulomb blockade
regime. For vanishing magnetic fields, the conductance peak height statistics
is found to be independent of the interactions strength. It is identical to the
statistics predicted by constant interaction single electron random matrix
theory and agrees well with recent experiments. However, in contrast to these
random matrix theories, our calculations reproduces the reduced sensitivity to
magnetic flux observed in many experiments. The relevant physics is traced to
the short range Coulomb correlations providing thus a unified explanation for
the transmission statistics as well as for the large conductance peak spacing
fluctuations observed in other experiments.Comment: Final version as publishe
Energy Level Statistics of Quantum Dots
We investigate the charging energy level statistics of disordered interacting
electrons in quantum dots by numerical calculations using the Hartree
approximation. The aim is to obtain a global picture of the statistics as a
function of disorder and interaction strengths. We find Poisson statistics at
very strong disorder, Wigner- Dyson statistics for weak disorder and
interactions, and a Gaussian intermediate regime. These regimes are as expected
from previous studies and fundamental considerations, but we also find
interesting and rather broad crossover regimes. In particular, intermediate
between the Gaussian and Poisson regimes we find a two-sided exponential
distribution for the energy level spacings. In comparing with experiment, we
find that this distribution may be realized in some quantum dots.Comment: 21 pages 10 figure
Statistics of conductance oscillations of a quantum dot in the Coulomb-blockade regime
The fluctuations and the distribution of the conductance peak spacings of a
quantum dot in the Coulomb-blockade regime are studied and compared with the
predictions of random matrix theory (RMT). The experimental data were obtained
in transport measurements performed on a semiconductor quantum dot fabricated
in a GaAs-AlGaAs heterostructure. It is found that the fluctuations in the peak
spacings are considerably larger than the mean level spacing in the quantum
dot. The distribution of the spacings appears Gaussian both for zero and for
non-zero magnetic field and deviates strongly from the RMT-predictions.Comment: 7 pages, 4 figure
Evanescent wave approach to diffractive phenomena in convex billiards with corners
What we are going to call in this paper "diffractive phenomena" in billiards
is far from being deeply understood. These are sorts of singularities that, for
example, some kind of corners introduce in the energy eigenfunctions. In this
paper we use the well-known scaling quantization procedure to study them. We
show how the scaling method can be applied to convex billiards with corners,
taking into account the strong diffraction at them and the techniques needed to
solve their Helmholtz equation. As an example we study a classically
pseudointegrable billiard, the truncated triangle. Then we focus our attention
on the spectral behavior. A numerical study of the statistical properties of
high-lying energy levels is carried out. It is found that all computed
statistical quantities are roughly described by the so-called semi-Poisson
statistics, but it is not clear whether the semi-Poisson statistics is the
correct one in the semiclassical limit.Comment: 7 pages, 8 figure
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