7,072 research outputs found
Oceanic terranes of S-Central America - 200 Million years of accretion history recorded on the W-edge of the Caribbean Plate
Contact resistance dependence of crossed Andreev reflection
We show experimentally that in nanometer scaled superconductor/normal metal
hybrid devices and in a small window of contact resistances, crossed Andreev
reflection (CAR) can dominate the nonlocal transport for all energies below the
superconducting gap. Besides CAR, elastic cotunneling (EC) and nonlocal charge
imbalance (CI) can be identified as competing subgap transport mechanisms in
temperature dependent four-terminal nonlocal measurements. We demonstrate a
systematic change of the nonlocal resistance vs. bias characteristics with
increasing contact resistances, which can be varied in the fabrication process.
For samples with higher contact resistances, CAR is weakened relative to EC in
the midgap regime, possibly due to dynamical Coulomb blockade. Gaining control
of CAR is an important step towards the realization of a solid state entangler.Comment: 5 pages, 4 figures, submitted to PR
Scavenger 0.1: A Theorem Prover Based on Conflict Resolution
This paper introduces Scavenger, the first theorem prover for pure
first-order logic without equality based on the new conflict resolution
calculus. Conflict resolution has a restricted resolution inference rule that
resembles (a first-order generalization of) unit propagation as well as a rule
for assuming decision literals and a rule for deriving new clauses by (a
first-order generalization of) conflict-driven clause learning.Comment: Published at CADE 201
On Some Positivity Properties of the Interquark Potential in QCD
We prove that the Fourier transform of the exponential e^{-\b V(R)} of the
{\bf static} interquark potential in QCD is positive. It has been shown by
Eliott Lieb some time ago that this property allows in the same limit of static
spin independent potential proving certain mass relation between baryons with
different quark flavors.Comment: 6 pages, latex with one postscript figur
Hierarchic Superposition Revisited
Many applications of automated deduction require reasoning in first-order
logic modulo background theories, in particular some form of integer
arithmetic. A major unsolved research challenge is to design theorem provers
that are "reasonably complete" even in the presence of free function symbols
ranging into a background theory sort. The hierarchic superposition calculus of
Bachmair, Ganzinger, and Waldmann already supports such symbols, but, as we
demonstrate, not optimally. This paper aims to rectify the situation by
introducing a novel form of clause abstraction, a core component in the
hierarchic superposition calculus for transforming clauses into a form needed
for internal operation. We argue for the benefits of the resulting calculus and
provide two new completeness results: one for the fragment where all
background-sorted terms are ground and another one for a special case of linear
(integer or rational) arithmetic as a background theory
Magnetoresistence engineering and singlet/triplet switching in InAs nanowire quantum dots with ferromagnetic sidegates
We present magnetoresistance (MR) experiments on an InAs nanowire quantum dot
device with two ferromagnetic sidegates (FSGs) in a split-gate geometry. The
wire segment can be electrically tuned to a single dot or to a double dot
regime using the FSGs and a backgate. In both regimes we find a strong MR and a
sharp MR switching of up to 25\% at the field at which the magnetizations of
the FSGs are inverted by the external field. The sign and amplitude of the MR
and the MR switching can both be tuned electrically by the FSGs. In a double
dot regime close to pinch-off we find {\it two} sharp transitions in the
conductance, reminiscent of tunneling MR (TMR) between two ferromagnetic
contacts, with one transition near zero and one at the FSG switching fields.
These surprisingly rich characteristics we explain in several simple resonant
tunneling models. For example, the TMR-like MR can be understood as a
stray-field controlled transition between singlet and a triplet double dot
states. Such local magnetic fields are the key elements in various proposals to
engineer novel states of matter and may be used for testing electron spin-based
Bell inequalities.Comment: 7 pages, 6 figure
A second eigenvalue bound for the Dirichlet Schroedinger operator
Let be the th eigenvalue of the Schr\"odinger
operator with Dirichlet boundary conditions on a bounded domain and with the positive potential . Following the spirit of the
Payne-P\'olya-Weinberger conjecture and under some convexity assumptions on the
spherically rearranged potential , we prove that . Here denotes the ball, centered at the
origin, that satisfies the condition .
Further we prove under the same convexity assumptions on a spherically
symmetric potential , that decreases
when the radius of the ball increases.
We conclude with several results about the first two eigenvalues of the
Laplace operator with respect to a measure of Gaussian or inverted Gaussian
density
Wet etch methods for InAs nanowire patterning and self-aligned electrical contacts
Advanced synthesis of semiconductor nanowires (NWs) enables their application
in diverse fields, notably in chemical and electrical sensing, photovoltaics,
or quantum electronic devices. In particular, Indium Arsenide (InAs) NWs are an
ideal platform for quantum devices, e.g. they may host topological Majorana
states. While the synthesis has been continously perfected, only few techniques
were developed to tailor individual NWs after growth. Here we present three wet
chemical etch methods for the post-growth morphological engineering of InAs NWs
on the sub-100 nm scale. The first two methods allow the formation of
self-aligned electrical contacts to etched NWs, while the third method results
in conical shaped NW profiles ideal for creating smooth electrical potential
gradients and shallow barriers. Low temperature experiments show that NWs with
etched segments have stable transport characteristics and can serve as building
blocks of quantum electronic devices. As an example we report the formation of
a single electrically stable quantum dot between two etched NW segments.Comment: 9 pages, 5 figure
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