1,014 research outputs found
The problem of uniqueness in the reduced description of adsorption on the wedge-shaped substrate
In the reduced one-dimensional description of the adsorption on the
wedge-shaped substrate the mid-point interface height serves as the order
parameter. We point at the ambiguity which appears in the transfer-matrix
approach to this problem. We also propose how to avoid this problem by
introducing the appropriate order parameter.Comment: 7 pages, 4 Postscript figures, uses psfrag.sty; double reference
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Origin of dips in tunneling dI/dV characteristics of cuprates
Extensive efforts have been made to understand the electronic properties of
high-Tc superconductors. One feature which has been discussed in the literature
during the past few years is the dips in tunneling conductances obtained in
cuprates. In this contribution, we focus our attention on the origin of these
dips. On the basis of experimental data obtained in Bi2Sr2CaCu2O8 and
YBa2Cu3O7, we show that the dips appear naturally in tunneling spectra due to a
superposition of the peaks and humps and, therefore, have no physical meaning.Comment: 2 pages including 3 figures. To appear in Physica C (proceedings of
the M2S-VIII Dresden Conference
A possible scenario for the mechanism of high-Tc superconductivity based on experimental data
The issue of the mechanism of high-Tc superconductivity remains open. In this
contribution, we propose a new scenario for the mechanism of superconductivity
in cuprates based on analysis of experimental data, mainly tunneling, neutron
scattering and muon-spin-relaxation data, made earlier (see e.g. Mod. Phys.
Lett. B 19 (2005) 743). A specific feature of this scenario is the mechanism of
the establishment of long-range phase coherence among Cooper pairs, based on
recent experimental data obtained in nonsuperconducting materials.Comment: 2 pages with 2 figures (Dresden conference
The oxygen isotope effect on critical temperature in superconducting copper oxides
The isotope effect provided a crucial key to the development of the BCS
(Bardeen-Cooper-Schrieffer) microscopic theory of superconductivity for
conventional superconductors. In superconducting cooper oxides (cuprates)
showing an unconventional type of superconductivity, the oxygen isotope effect
is very peculiar: the exponential coefficient strongly depends on doping level.
No consensus has been reached so far on the origin of the isotope effect in the
cuprates. Here we show that the oxygen isotope effect in cuprates is in
agreement with the bisoliton theory of superconductivity.Comment: 3 pages including 4 figures; version 2 is with minor correction
Noninvasiveness and time symmetry of weak measurements
Measurements in classical and quantum physics are described in fundamentally
different ways. Nevertheless, one can formally define similar measurement
procedures with respect to the disturbance they cause. Obviously, strong
measurements, both classical and quantum, are invasive -- they disturb the
measured system. We show that it is possible to define general weak
measurements, which are noninvasive: the disturbance becomes negligible as the
measurement strength goes to zero. Classical intuition suggests that
noninvasive measurements should be time symmetric (if the system dynamics is
reversible) and we confirm that correlations are time-reversal symmetric in the
classical case. However, quantum weak measurements -- defined analogously to
their classical counterparts -- can be noninvasive but not time symmetric. We
present a simple example of measurements on a two-level system which violates
time symmetry and propose an experiment with quantum dots to measure the
time-symmetry violation in a third-order current correlation function.Comment: 19 pages, 5 figures, more information at
http://www.fuw.edu.pl/~abednorz/tasym
Interfacial fluctuations near the critical filling transition
We propose a method to describe the short-distance behavior of an interface
fluctuating in the presence of the wedge-shaped substrate near the critical
filling transition. Two different length scales determined by the average
height of the interface at the wedge center can be identified. On one length
scale the one-dimensional approximation of Parry et al. \cite{Parry} which
allows to find the interfacial critical exponents is extracted from the full
description. On the other scale the short-distance fluctuations are analyzed by
the mean-field theory.Comment: 13 pages, 3 figure
Bosonic versus fermionic pairs of topological spin defects in monolayered high-T_c superconductors
The energy associated with bosonic and fermionic pairs of topological spin
defects in doped antiferromagnetic quantum spin-1/2 square lattice is estimated
within a resonating valence bond scenario, as described by a t-t'-J-like model
Hamiltonian, plus a t-perpendicular, responsible of a three-dimensional
screening of the electrostatic repulsion within the bosonic pairs. For
parameters appropriate for monolayered high-T_c superconductors, both fermionic
and bosonic pairs show x^2-y^2 symmetry. We find a critical value of doping
such that the energy of the bosonic pairs goes below twice the energy of two
fermionic pairs at their Fermi level. This finding could be related to the
onset of high-T_c superconductivity.Comment: 10 pages, 6 figures. To be published in Phys. Rev.
Violation of Leggett-Garg inequalities in quantum measurements with variable resolution and back-action
Quantum mechanics violates Leggett-Garg inequalities because the operator
formalism predicts correlations between different spin components that would
correspond to negative joint probabilities for the outcomes of joint
measurements. However, the uncertainty principle ensures that such joint
measurements cannot be implemented without errors. In a sequential measurement
of the spin components, the resolution and back-action errors of the
intermediate measurement can be described by random spin flips acting on an
intrinsic joint probability. If the error rates are known, the intrinsic joint
probability can be reconstructed from the noisy statistics of the actual
measurement outcomes. In this paper, we use the spin-flip model of measurement
errors to analyze experimental data on photon polarization obtained with an
interferometric setup that allows us to vary the measurement strength and hence
the balance between resolution and back-action errors. We confirm that the
intrinsic joint probability obtained from the experimental data is independent
of measurement strength and show that the same violation of the Leggett-Garg
inequality can be obtained for any combination of measurement resolution and
back-action.Comment: 17 pages, 7 figure
Optical differentiation between cashmere and other textile fibres by laser diffraction
This paper reports a novel method to differentiate cashmere from synthetic fibres and even from other wool fibres with the help of laser diffraction patterns. In the diffraction pattern, only natural fibres depict additional spots above and below the actual diffraction plane. These spots can be used to distinguish different fibre materials by comparing their length-to-height aspect ratio with standard values. Especially, it can be recognized that the diffraction lines above and below the diffraction plane are significantly longer and finer for cashmere fibres than for any other wool
Doping dependence of the mass enhancement in (Pb,Bi)_2 Sr_2 Ca Cu_2 O_8 at the antinodal point in the superconducting and normal state
Angle-resolved photoemission spectroscopy (ARPES) is used to study the mass
renormalization of the charge carriers in the high-T_c superconductor
(Pb,Bi)_2Sr_2CaCu_2O_8 in the vicinity of the (pi,0) point in the
superconducting and the normal state. Using matrix element effects at different
photon energies and due to a high momentum and energy resolution the bonding
and the antibonding bands could be separated in the whole dopant range. A huge
anisotropic coupling to a bosonic collective mode is observed below T_c for
both bands in particular for the underdoped case. Above T_c, the more isotropic
coupling to a continuum or a mode at much higher energy is significantly
weaker.Comment: 4 revtex pages, 4 eps figure
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