836 research outputs found
Spin splitting of X-related donor impurity states in an AlAs barrier
We use magnetotunneling spectroscopy to observe the spin splitting of the
ground state of an X-valley-related Si-donor impurity in an AlAs barrier. We
determine the absolute magnitude of the effective Zeeman spin splitting factors
of the impurity ground state to be g= 2.2 0.1. We also investigate
the spatial form of the electron wave function of the donor ground state, which
is anisotropic in the growth plane
Magnetic-field-induced singularities in spin dependent tunneling through InAs quantum dots
Current steps attributed to resonant tunneling through individual InAs
quantum dots embedded in a GaAs-AlAs-GaAs tunneling device are investigated
experimentally in magnetic fields up to 28 T. The steps evolve into strongly
enhanced current peaks in high fields. This can be understood as a
field-induced Fermi-edge singularity due to the Coulomb interaction between the
tunneling electron on the quantum dot and the partly spin polarized Fermi sea
in the Landau quantized three-dimensional emitter.Comment: 5 pages, 4 figure
Strong quantum memory at resonant Fermi edges revealed by shot noise
Studies of non-equilibrium current fluctuations enable assessing correlations
involved in quantum transport through nanoscale conductors. They provide
additional information to the mean current on charge statistics and the
presence of coherence, dissipation, disorder, or entanglement. Shot noise,
being a temporal integral of the current autocorrelation function, reveals
dynamical information. In particular, it detects presence of non-Markovian
dynamics, i.e., memory, within open systems, which has been subject of many
current theoretical studies. We report on low-temperature shot noise
measurements of electronic transport through InAs quantum dots in the
Fermi-edge singularity regime and show that it exhibits strong memory effects
caused by quantum correlations between the dot and fermionic reservoirs. Our
work, apart from addressing noise in archetypical strongly correlated system of
prime interest, discloses generic quantum dynamical mechanism occurring at
interacting resonant Fermi edges.Comment: 6 pages, 3 figure
Analysis of Granular Packing Structure by Scattering of THz Radiation
Scattering methods are widespread used to characterize the structure and
constituents of matter on small length scales. This motivates this introductory
text on identifying prospective approaches to scattering-based methods for
granular media. A survey to light scattering by particles and particle
ensembles is given. It is elaborated why the established scattering methods
using X-rays and visible light cannot in general be transferred to granular
media. Spectroscopic measurements using Terahertz radiation are highlighted as
they to probe the scattering properties of granular media, which are sensitive
to the packing structure. Experimental details to optimize spectrometer for
measurements on granular media are discussed. We perform transmission
measurements on static and agitated granular media using Fourier-transform
spectroscopy at the THz beamline of the BessyII storage ring. The measurements
demonstrate the potential to evaluate degrees of order in the media and to
track transient structural states in agitated bulk granular media.Comment: 12 Pages, 9 Figures, 56 Reference
On the Inequivalence of Weak-Localization and Coherent Backscattering
We define a current-conserving approximation for the local conductivity
tensor of a disordered system which includes the effects of weak localization.
Using this approximation we show that the weak localization effect in
conductance is not obtained simply from the diagram corresponding to the
coherent back-scattering peak observed in optical experiments. Other diagrams
contribute to the effect at the same order and decrease its value. These
diagrams appear to have no semiclassical analogues, a fact which may have
implications for the semiclassical theory of chaotic systems. The effects of
discrete symmetries on weak localization in disordered conductors is evaluated
and and compared to results from chaotic scatterers.Comment: 24 pages revtex + 12 figures on request; hub.94.
Criticality Analysis of Activity Networks under Interval Uncertainty
Dedicated to the memory of Professor Stefan Chanas - The extended abstract version of this paper has appeared in Proceedings of 11th International Conference on Principles and Practice of Constraint Programming (CP2005) ("Interval Analysis in Scheduling", Fortin et al. 2005)International audienceThis paper reconsiders the Project Evaluation and Review Technique (PERT) scheduling problem when information about task duration is incomplete. We model uncertainty on task durations by intervals. With this problem formulation, our goal is to assert possible and necessary criticality of the different tasks and to compute their possible earliest starting dates, latest starting dates, and floats. This paper combines various results and provides a complete solution to the problem. We present the complexity results of all considered subproblems and efficient algorithms to solve them
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