1,842 research outputs found
Determination of characteristic relaxation times and their significance in glassy disordered insulators
We revisit the field effect procedure used to characterise the slow dynamics
of glassy Anderson insulators. It is shown that in the slowest systems the
procedure fails and the "characteristic" time values extracted are not
intrinsic but determined by the experimental procedure itself. In other cases
(like lightly doped indium oxide) qualitative indications about the dynamics
might be obtained, however the times extracted cannot be seen as characteristic
relaxation times of the system in any simple manner, and more complete
experiments are necessary. Implications regarding the effect of carrier
concentration on the emergence of glassiness are briefly outlined.Comment: published with minor proof correction
Idiopathic True Aneurysm of the Radial Artery: A Rare Entity
AbstractIntroductionTrue aneurysms of the radial artery are extremely rare. Most cases of Radial artery aneurysm are the result of iatrogenic trauma, however other rare causes such as vascular tumours, connective tissue diseases and occupational injury have also been reported.Case reportA 60-year-old man presented with a pulsating mass in the anatomical snuffbox of the left hand. He underwent distal radial artery ligation and excision of the aneurysm. Histopathology demonstrated this to be a true aneurysm in continuation with the vessel wall.DiscussionThere are only a few cases of true distal radial artery aneurysm described in the literature. Careful examination and pre-operative imaging will help determine the most appropriate surgical management, including the need for vascular reconstruction
Absence of weak antilocalization in ferromagnetic films
We present magnetoresistance measurements performed on ultrathin films of
amorphous Ni and Fe. In these films the Curie temperature drops to zero at
small thickness, making it possible to study the effect of ferromagnetism on
localization. We find that non-ferromagnetic films are characterized by
positive magnetoresistance. This is interpreted as resulting from weak
antilocalization due to strong Bychkov-Rashba spin orbit scattering. As the
films become ferromagnetic the magnetoresistance changes sign and becomes
negative. We analyze our data to identify the individual contributions of weak
localization, weak antilocalization and anisotropic magnetoresistance and
conclude that the magnetic order suppresses the influence of spin-orbit effects
on localization phenomena in agreement with theoretical predictions.Comment: 6 pages, 6 figure
Universal transport in 2D granular superconductors
The transport properties of quench condensed granular superconductors are
presented and analyzed. These systems exhibit transitions from insulating to
superconducting behavior as a function of inter-grain spacing.
Superconductivity is characterized by broad transitions in which the resistance
drops exponentially with reducing temperature. The slope of the log R versus T
curves turns out to be universaly dependent on the normal state film resistance
for all measured granular systems. It does not depend on the material, critical
temperature, geometry, or experimental set-up. We discuss possible physical
scenarios to explain these findings.Comment: 4 pages, 3 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
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
Niobium superconducting nanowire single-photon detectors
We investigate the performance of superconducting nanowire photon detectors
fabricated from ultra-thin Nb. A direct comparison is made between these
detectors and similar nanowire detectors fabricated from NbN. We find that Nb
detectors are significantly more susceptible than NbN to thermal instability
(latching) at high bias. We show that the devices can be stabilized by reducing
the input resistance of the readout. Nb detectors optimized in this way are
shown to have approximately 2/3 the reset time of similar large-active-area NbN
detectors of the same geometry, with approximately 6% detection efficiency for
single photons at 470 nm
Reset dynamics and latching in niobium superconducting nanowire single-photon detectors
We study the reset dynamics of niobium (Nb) superconducting nanowire
single-photon detectors (SNSPDs) using experimental measurements and numerical
simulations. The numerical simulations of the detection dynamics agree well
with experimental measurements, using independently determined parameters in
the simulations. We find that if the photon-induced hotspot cools too slowly,
the device will latch into a dc resistive state. To avoid latching, the time
for the hotspot to cool must be short compared to the inductive time constant
that governs the resetting of the current in the device after hotspot
formation. From simulations of the energy relaxation process, we find that the
hotspot cooling time is determined primarily by the temperature-dependent
electron-phonon inelastic time. Latching prevents reset and precludes
subsequent photon detection. Fast resetting to the superconducting state is
therefore essential, and we demonstrate experimentally how this is achieved
Nernst Sign-Reversal in the Hexatic Vortex Phase of Weakly Disordered a-MoGe Thin Films
The hexatic phase is an intermediate stage in the melting process of a 2D
crystal due to topological defects. Recently, this exotic phase was
experimentally identified in the vortex lattice of 2D weakly disordered
superconducting MoGe by scanning tunneling microscopic measurements. Here we
study this vortex state by the Nernst effect, which is an effective and
sensitive tool to detect vortex motion, especially in the superconducting
fluctuation regime. We find a surprising Nernst sign reversal at the melting
transition of the hexatic phase. We propose that they are a consequence of
vortex dislocations in the hexatic state which diffuse preferably from the cold
to hot.Comment: 8 pages, 8 figure
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