53,551 research outputs found
Enhancement of Coherent X ray Diffraction from Nanocrystals by Introduction of X ray Optics
Coherent X-ray Diffraction is applied to investigate the structure of individual nanocrystalline silver particles in the 100nm size range. In order to enhance the available signal, Kirkpatrick-Baez focusing optics have been introduced in the 34-ID-C beamline at APS. Concerns about the preservation of coherence under these circumstances are addressed through experiment and by calculations
Andreev transport in two-dimensional normal-superconducting systems in strong magnetic fields
The conductance in two-dimensional (2D) normal-superconducting (NS) systems
is analyzed in the limit of strong magnetic fields when the transport is
mediated by the electron-hole states bound to the sample edges and NS
interface, i.e., in the Integer Quantum Hall Effect regime.The Andreev-type
process of the conversion of the quasiparticle current into the superflow is
shown to be strongly affected by the mixing of the edge states localized at the
NS and insulating boundaries. The magnetoconductance in 2D NS structures is
calculated for both quadratic and Dirac-like normal state spectra. Assuming a
random scattering of the edge modes we analyze both the average value and
fluctuations of conductance for an arbitrary number of conducting channels.Comment: 5 pages, 1 figur
3D MODELING AND DATA ENRICHMENT IN DIGITAL RECONSTRUCTION OF ARCHITECTURAL HERITAGE
The paper presents some experiments carried out as part of the virtual reconstruction of buildings just documented by partial sketches, or partially built, or no more existing, with the aim (a) to emphasize the use of a semantic construction of the digital model, not only as a means to modeling a building but as a cognitive system, (b) to show conceptual similarity between the treaties and BIM, (c) to propose new and more robust solutions to the 3D modeling from 2D drawings for CH artifacts, able to allow the verification of the assumptions used during the reconstruction pipeline, (d) to make use of interactive technical reference, typically real-time photorealistic rendering, for the visualization of three-dimensional model and of variants snapshots, managed by an iconic for illustrating the method of comparison and guided reading of model's characters of the steps taken
Large magneto-thermal effect and the spin-phonon coupling in a parent insulating cuprate Pr_{1.3}La_{0.7}CuO_4
The magnetic-field (H) dependence of the thermal conductivity \kappa of
Pr_{1.3}La_{0.7}CuO_4 is found to show a pronounced minimum for in-plane fields
at low temperature, which is best attributed to the scattering of phonons by
free spins that are seen by a Schottky-type specific heat and a Curie-Weiss
susceptibility. Besides pointing to a strong spin-phonon coupling in cuprates,
the present result demonstrates that the H-dependence of the phonon heat
transport should not be naively neglected when discussing the \kappa(H)
behavior of cuprates, since the Schottky anomaly is ubiquitously found in
cuprates at any doping.Comment: 6 pages, 4 figures, accepted for publication in Phys. Rev.
High-Fidelity Readout in Circuit Quantum Electrodynamics Using the Jaynes-Cummings Nonlinearity
We demonstrate a qubit readout scheme that exploits the Jaynes-Cummings
nonlinearity of a superconducting cavity coupled to transmon qubits. We find
that in the strongly-driven dispersive regime of this system, there is the
unexpected onset of a high-transmission "bright" state at a critical power
which depends sensitively on the initial qubit state. A simple and robust
measurement protocol exploiting this effect achieves a single-shot fidelity of
87% using a conventional sample design and experimental setup, and at least 61%
fidelity to joint correlations of three qubits.Comment: 5 pages, 4 figure
Pressure coefficients of Raman modes of carbon nanotubes resolved by chirality: Environmental effect on graphene sheet
Studies of the mechanical properties of single-walled carbon nanotubes are
hindered by the availability only of ensembles of tubes with a range of
diameters. Tunable Raman excitation spectroscopy picks out identifiable tubes.
Under high pressure, the radial breathing mode shows a strong environmental
effect shown here to be largely independent of the nature of the environment .
For the G-mode, the pressure coefficient varies with diameter consistent with
the thick-wall tube model. However, results show an unexpectedly strong
environmental effect on the pressure coefficients. Reappraisal of data for
graphene and graphite gives the G-mode Grueuneisen parameter gamma = 1.34 and
the shear deformation parameter beta = 1.34.Comment: Submitted to Physical Review
Microwave-induced pi-junction transition in a superconductor / quantum-dot / superconductor structure
Using the nonequilibrium Green function, we show that microwave irradiation
can reverse the supercurrent flowing through a superconductor / quantum-dot /
superconductor structure. In contrast with the conventional sideband effect in
normal-metal / quantum-dot / normal-metal junctions, the photon-assisted
structures appear near ,
where is the resonant energy level of the quantum dot and is
the frequency of microwave field. Each photon-assisted structure is composed of
a negative and a positive peak, with an abrupt jump from the negative peak to
the positive peak around . The
microwave-induced -junction transition is interpreted in the picture of
photon-assisted Andreev bound states, which are formed due to multiple
photon-assisted Andreev reflection between the two superconductors. Moreover,
the main resonance located at can also be reversed with proper
microwave strength and frequency.Comment: 10 pagres, 3 figure
Response time of a normal-superconductor hybrid system under the step-like pulse bias
The response of a quantum dot coupled with one normal lead and a
superconductor lead driven by a step-like pulse bias is studied using the
non-equilibrium Green function method. In the linear pulse bias regime, the
responses of the upwards and downwards bias are symmetric. In this regime the
turn-on time and turn-off time are much slower than that of the normal system
due to the Andreev reflection. On the other hand, for the large pulse bias
, the instantaneous current exhibits oscillatory behaviors with the
frequency . The turn on/off times are in (or shorter than)
the scale of , so they are faster for the larger bias . In
addition, the responses for the upwards and downwards bias are asymmetric at
large . The turn-on time is larger than the turn-off time but the
relaxation time \cite{note1} depends only on the coupling strength and
it is much smaller than the turn-on/off times for the large bias .Comment: 8 pages, 4 figures, accepted for publication in Phys. Rev.
Conductance plateau in quantum spin transport through an interacting quantum dot
Quantum spin transport is studied in an interacting quantum dot. It is found
that a conductance "plateau" emerges in the non-linear charge conductance by a
spin bias in the Kondo regime. The conductance plateau, as a complementary to
the Kondo peak, originates from the strong electron correlation and exchange
processes in the quantum dot, and can be regarded as one of the characteristics
in quantum spin transport.Comment: 5 pages, 5 figure
- …