738 research outputs found
Ulta-slow relaxation in discontinuous-film based electron glasses
We present field effect measurements on discontinuous 2D thin films which are
composed of a sub monolayer of nano-grains of Au, Ni, Ag or Al. Like other
electron glasses these systems exhibit slow conductance relaxation and memory
effects. However, unlike other systems, the discontinuous films exhibit a
dramatic slowing down of the dynamics below a characteristic temperature .
is typically between 10-50K and is sample dependent. For the
sample exhibits a few other peculiar features such as repeatable conductance
fluctuations in millimeter size samples. We suggest that the enhanced system
sluggishness is related to the current carrying network becoming very dilute in
discontinuous films so that the system contains many parts which are
electrically very weakly connected and the transport is dominated by very few
weak links. This enables studying the glassy properties of the sample as it
transitions from a macroscopic sample to a mesocopic sample, hence, the results
provide new insight on the underlying physics of electron glasses.Comment: 4 pages, 4 figure
Coexistence of Coulomb blockade and zero bias anomaly in a strongly coupled quantum dot
The current-voltage characteristics through a metallic quantum dot which is
well coupled to a metallic lead are measured. It is shown that the I-V curves
are composed of two contributions. One is a suppression of the tunneling
conductivity at the Fermi level and the second is an oscillating feature which
shifts with gate voltage. The results indicate that Zero-Bias-Anomaly and
Coulomb Blockade phenomena coexist in an asymmetric strongly coupled quantum
dot.Comment: 4 pages, 4 figure
Is a multiple excitation of a single atom equivalent to a single excitation of an ensemble of atoms?
Recent technological advances have enabled to isolate, control and measure
the properties of a single atom, leading to the possibility to perform
statistics on the behavior of single quantum systems. These experiments have
enabled to check a question which was out of reach previously: Is the
statistics of a repeatedly excitation of an atom N times equivalent to a single
excitation of an ensemble of N atoms? We present a new method to analyze
quantum measurements which leads to the postulation that the answer is most
probably no. We discuss the merits of the analysis and its conclusion.Comment: 3 pages, 3 figure
Zero bias anomaly in a two dimensional granular insulator
We compare tunneling density of states (TDOS) into two ultrathin Ag films,
one uniform and one granular, for different degrees of disorder. The uniform
film shows a crossover from Altshuler-Aronov (AA) zero bias anomaly to Efros
Shklovskii (ES) like Coulomb gap as the disorder is increased. The granular
film, on the other hand, exhibits AA behavior even deeply in the insulating
regime. We analyze the data and find that granularity introduces a new regime
for the TDOS. While the conductivity is dominated by hopping between clusters
of grains and is thus insulating, the TDOS probes the properties of an
individual cluster which is "metallic".Comment: 4 pages, 4 figure
Hadamard magnetization transfers achieve dramatic sensitivity enhancements in homonuclear multidimensional NMR correlations of labile sites in proteins, polysaccharides and nucleic acids
EXSY, TOCSY and NOESY lie at the foundation of homonuclear NMR experiments in
organic and pharmaceutical chemistry, as well as in structural biology. Limited
magnetization transfer efficiency is an intrinsic downside of these methods,
particularly when targeting rapidly exchanging species such as labile protons
ubiquitous in polysaccharides, sidechains and backbones of proteins, and in
bases and sugars of nucleic acids: the fast decoherence imparted on these
protons through solvent exchanges, greatly reduces their involvement in
homonuclear correlation experiments. We have recently discussed how these
decoherences can be visualized as an Anti-Zeno Effect, that can be harnessed to
enhance the efficiency of homonuclear transfers within Looped PROjected
SpectroscopY (L-PROSY) leading to 200-300% enhancements in NOESY and TOCSY
cross-peaks for amide groups in biomolecules. This study demonstrates that even
larger sensitivity gains per unit time, equivalent to reductions by several
hundred-folds in the duration of experiments, can be achieved by looping
inversion or using saturation procedures. In the ensuing experiments a priori
selected frequencies are encoded according to Hadamard recipes, and
subsequently resolved along the indirect dimension via linear combinations.
Magnetization-transfer (MT) processes reminiscent of those occurring in CEST
provide significant enhancements in the resulting cross-peaks, in only a
fraction of acquisition time of a normal 2D experiment. The effectiveness of
the ensuing three-way polarization transfer interplay between water, labile and
non-labile protons was corroborated experimentally for proteins,
homo-oligosaccharides and nucleic acids. In all cases, cross-peaks barely
detectable in conventional 2D NMR counterparts, were measured ca. 10-fold
faster and with 200-600% signal enhancements by the Hadamard MT counterparts
Percolation model for the superconductor-insulator transition in granular films
We study the temperature dependence of the superconductor-insulator
transition in granular superconductors. Empirically, these systems are
characterized by very broad resistance tails, which depend exponentially on the
temperature, and the normal state resistance. We model these systems by a
two-dimensional random resistor percolation networks in which the resistance
between two grains is governed either by Josephson junction coupling or by
quasi particle tunneling. Our numerical simulations as well as an effective
medium evaluation explain the experimental results over a wide range of
temperatures and resistances. Using effective medium approximation we find an
analytical expression for the effective resistance of the system and the value
of the critical resistance separating conducting from insulating branches.Comment: 4 pages, 2 figure
Subgap anomaly and above-energy-gap structure in chains of diffusive SNS junctions
We present the results of low-temperature transport measurements on chains of
superconductor--normal-constriction--superconductor (SNS) junctions fabricated
on the basis of superconducting PtSi film. A comparative study of the
properties of the chains, consisting of 3 and 20 SNS junctions in series, and
single SNS junctions reveals essential distinctions in the behavior of the
current-voltage characteristics of the systems: (i) the gradual decrease of the
effective suppression voltage for the excess conductivity observed at zero bias
as the quantity of the SNS junctions increases, (ii) a rich fine structure on
the dependences dV/dI-V at dc bias voltages higher than the superconducting gap
and corresponding to some multiples of 2\Delta/e. A model to explain this
above-energy-gap structure based on energy relaxation of electron via
Cooper-pair-breaking in superconducting island connecting normal metal
electrods is proposed.Comment: RevTex, 5 pages, 4 figure
Two-dimensional array of diffusive SNS junctions with high-transparent interfaces
We report the first comparative study of the properties of two-dimensional
arrays and single superconducting film - normal wire - superconducting film
(SNS) junctions. The NS interfaces of our SNS junctions are really high
transparent, for superconducting and normal metal parts are made from the same
material (superconducting polycrystalline PtSi film). We have found that the
two-dimensional arrays reveal some novel features: (i) the significant
narrowing of the zero bias anomaly (ZBA) in comparison with single SNS
junctions, (ii) the appearance of subharmonic energy gap structure (SGS), with
up to n=16 (eV=\pm 2\Delta/n), with some numbers being lost, (iii) the
transition from 2D logarithmic weak localization behavior to metallic one. Our
experiments show that coherent phenomena governed by the Andreev reflection are
not only maintained over the macroscopic scale but manifest novel pronounced
effects as well. The behavior of the ZBA and SGS in 2D array of SNS junctions
strongly suggests that the development of a novel theoretical approach is
needed which would self-consistently take into account the distribution of the
currents, the potentials, and the superconducting order parameter.Comment: RevTex, 5 pages, 5 figure
Privatization and State Capacity in Postcommunist Society
Economists have used cross-national regression analysis to argue that postcommunist economic failure is the result of inadequate adherence liberal economic policies. Sociologists have relied on case study data to show that postcommunist economic failure is the outcome of too close adherence to liberal policy recommendations, which has led to an erosion of state effectiveness, and thus produced poor economic performance. The present paper advances a version of this statist theory based on a quantitative analysis of mass privatization programs in the postcommunist world. We argue that rapid large-scale privatization creates severe supply and demand shocks for enterprises, thereby inducing firm failure. The resulting erosion of tax revenues leads to a fiscal crisis for the state, and severely weakens its capacity and bureaucratic character. This, in turn, reacts back on the enterprise sector, as the state can no longer support the institutions necessary for the effective functioning of a modern economy, thus resulting in deindustrialization. Using cross-national regression techniques we find that the implementation of mass privatization programs negatively impacts measures of economic growth, state capacity and the security of property rights.http://deepblue.lib.umich.edu/bitstream/2027.42/40192/3/wp806.pd
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