29,352 research outputs found
Scanning Tunneling Spectroscopy of Bi2Sr2CuO6+d: New Evidence for the Common Origin of the Pseudogap and Superconductivity
Using scanning tunneling spectroscopy, we investigated the temperature dependence of the quasiparticle density of states of overdoped Bi2Sr2CuO6+ÎŽ between 275 mK and 82 K. Below Tc = 10 K, the spectra show a gap with well-defined coherence peaks at ±Îpâ12 meV, which disappear at Tc. Above Tc, the spectra display a clear pseudogap of the same magnitude, gradually filling up and vanishing at T*â68 K. The comparison with Bi2Sr2CaCu2O8+ÎŽ demonstrates that the pseudogap and the superconducting gap scale with each other, providing strong evidence that they have a common origin
Linear and field-independent relation between vortex core state energy and gap in Bi2Sr2CaCu2O8+d
We present a scanning tunneling spectroscopy study on quasiparticle states in vortex cores in Bi2Sr2CaCu2O8+ÎŽ. The energy of the observed vortex core states shows an approximately linear scaling with the superconducting gap in the region just outside the core. This clearly distinguishes them from conventional localized core states and is a signature of the mechanism responsible for their discrete appearance in high-temperature superconductors. The energy scaling of the vortex core states also suggests a common nature of vortex cores in Bi2Sr2CaCu2O8+ÎŽ and YBa2Cu3O7-ÎŽ. Finally, these states do not show any dependence on the applied magnetic field between 1 and 6 T
Four-point measurements of n- and p-type two-dimensional systems fabricated with cleaved-edge overgrowth
We demonstrate a contact design that allows four-terminal magnetotransport
measurements of cleaved-edge overgrown two-dimensional electron and hole
systems. By lithographically patterning and etching a bulk-doped surface layer,
finger-shaped leads are fabricated, which contact the two-dimensional systems
on the cleave facet. Both n- and p-type two-dimensional systems are
demonstrated at the cleaved edge, using Si as either donor or acceptor,
dependent on the growth conditions. Four-point measurements of both gated and
modulation-doped samples yield fractional quantum Hall features for both n- and
p-type, with several higher-order fractions evident in n-type modulation-doped
samples.Comment: 3 pages, 3 figure
A survey of backward proton and pion production in p+C interactions at beam momenta from 1 to 400 GeV/c
New data on proton and pion production in p+C interactions from the CERN PS
and SPS accelerators are used in conjunction with other available data sets to
perform a comprehensive survey of backward hadronic cross sections. This survey
covers the complete backward hemisphere in the range of lab angles from 10 to
180 degrees, from 0.2 to 1.4 GeV/c in lab momentum and from 1 to 400 GeV/c in
projectile momentum. Using the constraints of continuity and smoothness of the
angular, momentum and energy dependences a consistent description of the
inclusive cross sections is established which allows the control of the
internal consistency of the nineteen available data sets.Comment: 52 pages 47 figure
Testing formula satisfaction
We study the query complexity of testing for properties defined by read once formulae, as instances of massively parametrized properties, and prove several testability and non-testability results. First we prove the testability of any property accepted by a Boolean read-once formula involving any bounded arity gates, with a number of queries exponential in \epsilon and independent of all other parameters. When the gates are limited to being monotone, we prove that there is an estimation algorithm, that outputs an approximation of the distance of the input from
satisfying the property. For formulae only involving And/Or gates, we provide a more efficient test whose query complexity is only quasi-polynomial in \epsilon. On the other hand we show that such testability results do not hold in general for formulae over non-Boolean alphabets; specifically we construct a property defined by a read-once arity 2 (non-Boolean) formula over alphabets of size 4, such that any 1/4-test for it requires a number of queries depending on the formula size
Optical Position Sensor Based on Digital Image Processing: Magnetic Field Mapping Improvement
Optical position measurement system for an automated magnetic field mapping apparatus based on fluxgate sensors is presented. For the exact position estimation of the sensor head, a simple smart camera was developed with respect to minimal hardware configuration and real-time execution of position measurement algorithm. The camera is observing the mapped scene and evaluates position of the sensor head using an active marker. The sensor head is designed as movable, what allows keeping the scene fixed and exactly referenced to the mapped magnetic field using coordinates obtained from image. With image sensor fixed 2.5 m above the plane and range ±130 mm around the lens optical axis (image center), the total position measurement error is less than 0.5 mm
Pressure-Induced Rotational Symmetry Breaking in URuSi
Phase transitions and symmetry are intimately linked. Melting of ice, for
example, restores translation invariance. The mysterious hidden order (HO)
phase of URuSi has, despite relentless research efforts, kept its
symmetry breaking element intangible. Here we present a high-resolution x-ray
diffraction study of the URuSi crystal structure as a function of
hydrostatic pressure. Below a critical pressure threshold kbar,
no tetragonal lattice symmetry breaking is observed even below the HO
transition K. For , however, a pressure-induced rotational
symmetry breaking is identified with an onset temperatures K.
The emergence of an orthorhombic phase is found and discussed in terms of an
electronic nematic order that appears unrelated to the HO, but with possible
relevance for the pressure-induced antiferromagnetic (AF) phase. Existing
theories describe the HO and AF phases through an adiabatic continuity of a
complex order parameter. Since none of these theories predicts a
pressure-induced nematic order, our finding adds an additional symmetry
breaking element to this long-standing problem.Comment: 6 pages, 4 figures and supplemental material
About multiplicities and applications to Bezout numbers
Let denote a local Noetherian ring and
an ideal such that for a
finitely generated -module . Let \au = a_1,\ldots,a_d denote a system
of parameters of such that for . It follows that \chi := e_0(\au;M)
- c \cdot e_0(\mathfrak{q};M) \geq 0, where .
The main results of the report are a discussion when resp. to
describe the value of in some particular cases. Applications concern
results on the multiplicity e_0(\au;M) and applications to Bezout numbers.Comment: 11 pages, to appear Springer INdAM-Series, Vol. 20 (2017
Deciding Quantifier-Free Presburger Formulas Using Parameterized Solution Bounds
Given a formula in quantifier-free Presburger arithmetic, if it has a
satisfying solution, there is one whose size, measured in bits, is polynomially
bounded in the size of the formula. In this paper, we consider a special class
of quantifier-free Presburger formulas in which most linear constraints are
difference (separation) constraints, and the non-difference constraints are
sparse. This class has been observed to commonly occur in software
verification. We derive a new solution bound in terms of parameters
characterizing the sparseness of linear constraints and the number of
non-difference constraints, in addition to traditional measures of formula
size. In particular, we show that the number of bits needed per integer
variable is linear in the number of non-difference constraints and logarithmic
in the number and size of non-zero coefficients in them, but is otherwise
independent of the total number of linear constraints in the formula. The
derived bound can be used in a decision procedure based on instantiating
integer variables over a finite domain and translating the input
quantifier-free Presburger formula to an equi-satisfiable Boolean formula,
which is then checked using a Boolean satisfiability solver. In addition to our
main theoretical result, we discuss several optimizations for deriving tighter
bounds in practice. Empirical evidence indicates that our decision procedure
can greatly outperform other decision procedures.Comment: 26 page
Exploring Biorthonormal Transformations of Pair-Correlation Functions in Atomic Structure Variational Calculations
Multiconfiguration expansions frequently target valence correlation and
correlation between valence electrons and the outermost core electrons.
Correlation within the core is often neglected. A large orbital basis is needed
to saturate both the valence and core-valence correlation effects. This in turn
leads to huge numbers of CSFs, many of which are unimportant. To avoid the
problems inherent to the use of a single common orthonormal orbital basis for
all correlation effects in the MCHF method, we propose to optimize independent
MCHF pair-correlation functions (PCFs), bringing their own orthonormal
one-electron basis. Each PCF is generated by allowing single- and double-
excitations from a multireference (MR) function. This computational scheme has
the advantage of using targeted and optimally localized orbital sets for each
PCF. These pair-correlation functions are coupled together and with each
component of the MR space through a low dimension generalized eigenvalue
problem. Nonorthogonal orbital sets being involved, the interaction and overlap
matrices are built using biorthonormal transformation of the coupled basis sets
followed by a counter-transformation of the PCF expansions.
Applied to the ground state of beryllium, the new method gives total energies
that are lower than the ones from traditional CAS-MCHF calculations using large
orbital active sets. It is fair to say that we now have the possibility to
account for, in a balanced way, correlation deep down in the atomic core in
variational calculations
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