451 research outputs found
On the determination of the quasiparticle scattering rate in unconventional superconductors by microwave surface impedance
In the approximation of validity of the Drude expression for quasiparticle
conductivity and the assumption that all electrons at T = 0 transform into a
superfluide condensate, the expression for the quasiparticle scattering rate
tau -1 in terms of the real and imaginary parts of the microwave surface
impedance has been obtained. The resulting expression is a generalization of
the well-known expression for tau^-1, valid for omega x tau is much less 1, to
an arbitrary value of omega x tau, where omega is the frequency of the
microwave field. From experimental Ka-band impedance measurements, temperature
dependence of tau^-1 in superconducting single crystal pnictides
Ba(Fe1-xCox)2As2 is obtained using the generalized expression. It is shown that
under condition of the given work, the approximation omega x tau is much less 1
gives the considerable error in determination of tau^-1.Comment: 3 pages, 1 figur
Tunable coaxial cavity resonator for linear and nonlinear microwave characterization of superconducting wires
We discuss experimental results obtained using a tunable cylindrical coaxial
cavity constituted by an outer Cu cylinder and an inner Pb-BSCCO wire. We have
used this device for investigating the microwave response of the
superconducting wire, both in the linear and nonlinear regimes. In particular,
by tuning the different modes of the cavity to make them resonant at exactly
harmonic frequencies, we have detected the power emitted by the superconducting
inner wire at the second- and third-harmonic frequency of the driving field.
The results obtained in the nonlinear regime, whether for the microwave surface
impedance or the harmonic emission, are qualitatively accounted for considering
intergrain fluxon dynamics. The use of this kind of device can be of strong
interest to investigate and characterise wires of large dimensions to be used
for implementing superconducting-based microwave devices.Comment: 14 pages, 6 embedded figures, accepted for publication in Supercond.
Sci. Techno
Simulation of boron diffusion during low-temperature annealing of implanted silicon
Modeling of ion-implanted boron redistribution in silicon crystals during
low-temperature annealing with a small thermal budget has been carried out. It
was shown that formation of "tails"' in the low-concentration region of
impurity profiles occurs due to the long-range migration of boron interstitialsComment: 16 pages, 3 figure
Unusual features in the nonlinear microwave surface impedance of Y-Ba-Cu-O thin films
Striking features have been found in the nonlinear microwave (8 GHz) surface
impedance of high-quality YBaCuO thin films with comparable
low power characteristics [ and ]. The surface resistance is found to increase,
decrease, or remain independent of the microwave field (up to 60 mT)
at different temperatures and for different samples. However, the surface
reactance always follows the same functional form. Mechanisms which may
be responsible for the observed variations in and are briefly
discussed.Comment: 4 pages, 4 figure
Pattern formation on the surface of cationic-anionic cylindrical aggregates
Charged pattern formation on the surfaces of self--assembled cylindrical
micelles formed from oppositely charged heterogeneous molecules such as
cationic and anionic peptide amphiphiles is investigated. The net
incompatibility among different components results in the formation of
segregated domains, whose growth is inhibited by electrostatics. The transition
to striped phases proceeds through an intermediate structure governed by
fluctuations, followed by states with various lamellar orientations, which
depend on cylinder radius and . We analyze the specific heat,
susceptibility , domain size and morphology as a
function of and .Comment: Sent to PRL 11Jan05 Transferred from PRL to PRE 10Jun0
Mechanisms of arsenic clustering in silicon
A model of arsenic clustering in silicon is proposed and analyzed. The main
feature of the proposed model is the assumption that negatively charged arsenic
complexes play a dominant role in the clustering process. To confirm this
assumption, electron density and concentration of impurity atoms incorporated
into the clusters are calculated as functions of the total arsenic
concentration. A number of the negatively charged clusters incorporating a
point defect and one or more arsenic atoms are investigated. It is shown that
for the doubly negatively charged clusters or for clusters incorporating more
than one arsenic atom the electron density reaches a maximum value and then
monotonically and slowly decreases as total arsenic concentration increases. In
the case of doubly negatively charged cluster incorporating two arsenic atoms,
the calculated electron density agrees well with the experimental data.
Agreement with the experiment confirms the conclusion that two arsenic atoms
participate in the cluster formation. Among all present models, the proposed
model of clustering by formation of doubly negatively charged cluster
incorporating two arsenic atoms gives the best fit to the experimental data and
can be used in simulation of high concentration arsenic diffusion.Comment: 13 pages, 4 figures. Revised and shortened version of the paper has
been published in Phys. Rev. B, Vol.74 (3), art. no. 035205 (2006
Nonlinear Dielectric Microwave Losses in MgO Substrates
We have investigated the nonlinear surface impedance and two-tone
intermodulation distortion of nine epitaxial YBa2Cu3O7-d films on MgO
substrates, using stripline resonators, at frequencies f=2.3-11.2GHz and
temperatures T=1.7K-Tc. The power dissipation decreased by up to one order of
magnitude as the microwave electric field was increased to about 100V/m for
T<20 K, while the reactance Xs showed only a weak increase. The minimum of the
losses correlated with a plateau in the intermodulation signal. The same
features were observed for a Nb film on MgO. The anomalous response is due to
nonlinear dielectric losses in the substrate, which can be described by defect
dipole relaxation
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