2,878 research outputs found
Influence of Disorder on the Hall Effect in BiSrCuO
The in-plane resistivity and Hall coefficient have been measured for the
single-layer compound BiSrCuO for the whole range of
doping states. The deviation of the Hall coefficient, , from a
high-temperature linear behavior and the temperature dependence of the Hall
angle are both only weakly dependent upon doping, contrasting with
BiSrLaCuO and BiSrCaCuO. This
is in contradiction with former proposals that the transverse transport detects
the formation of incoherent Cooper pairs in the pseudogap state. Conversely,
the analysis of the data using a phenomenological angular dependent scattering
rate clearly allows to distinguish between underdoped and overdoped states, and
we propose that the maximum in simply arises due to the combination of
a large isotropic scattering rate and an anisotropic temperature dependent one
Current dependent fluctuations in a BiSrCuO thin film
The current dependence of the excess conductivity is measured up to for a BiSrCuO thin film, as a function of doping. It
is found to be anomalously sensitive to the transport current and to behave as
a universal function of in the whole doping range. We discuss these
results in the perspective of a granular superconductor with a gapless-like
behavior
Magnetoresistance and Hall effect in e-doped superconducting SrLaCuO thin films
We have epitaxially grown c-axis oriented SrxLa1-xCuO2 thin films by rf
sputtering on KTaO3 substrates with x = 0.12. The as-grown deposits are
insulating and a series of superconducting films with various Tc(R=0) up to 26
K have been obtained by in-situ oxygen reduction. Transport measurements in the
ab plane of these samples have been undertaken. We report original results on
the temperature dependence of the Hall effect and on the anisotropic
magnetoresistance (T > Tc). We discuss the magnitude of upper critical fields
and anisotropy, the Hall effect, which presents changes of sign indicative of
the existence of two types of carriers, the normal state magnetoresistance,
negative in parallel magnetic field, a possible signature of spin scattering.
These properties are compared to those of hole-doped cuprates, such as
BiSr(La)CuO with comparable Tc.Comment: 4 pages, 4 figures; to appear in Proceedings of LT25, Journal of
Physics : Conference Serie
Penetration depth of electron-doped-infinite-layer SrLaCuO thin films
The in-plane penetration depth of SrLaCuO thin
films at various doping obtained from oxygen reduction has been measured, using
AC susceptibility measurements. For the higher doping samples, the superfluid
density deviates strongly from the s-wave behavior, suggesting, in analogy with
other electron-doped cuprates, a contribution from a nodal hole pocket, or a
small gap on the Fermi surface such as an anisotropic s-wave order parameter.
The low value of the superfluid densities, likely due to a strong
doping-induced disorder, places the superconducting transition of our samples
in the phase-fluctuation regime
Upper critical field from normal state fluctuations in BiSrCuO
The in-plane magnetoresistance of an epitaxial BiSrCuO
thin film was systematically investigated as a function of doping, above .
The orbital magnetoconductance is used to extract the crossover field line
in the fluctuation regime. This field is found in good agreement
with the upper critical field obtained from resistivity data below , and
exhibits a similar upward curvature, thus pointing toward the existence of a
critical correlation length. The consequences regarding the nature of the
resistive transition are discussed
Calorimetric Investigation of CeRu2Ge2 up to 8 GPa
We have developed a calorimeter able to give a qualitative picture of the
specific heat of a sample under high pressure up to approximately 10 GPa. The
principle of ac-calorimetry was adapted to the conditions in a high pressure
clamp. The performance of this technique was successfully tested with the
measurement of the specific heat of CeRu2Ge2 in the temperature range 1.5
K<T<12 K. The phase diagram of its magnetic phases is consistent with previous
transport measurements.Comment: 5 pages, 4 figure
Anisotropic properties of MgB2 by torque magnetometry
Anisotropic properties of superconducting MgB2 obtained by torque
magnetometry are compared to theoretical predictions, concentrating on two
issues. Firstly, the angular dependence of Hc2 is shown to deviate close to Tc
from the dependence assumed by anisotropic Ginzburg-Landau theory. Secondly,
from the evaluation of torque vs angle curves it is concluded that the
anisotropy of the penetration depth gamma_lambda has to be substantially higher
at low temperature than theoretical estimates, at least in fields higher than
0.2 T.Comment: 2 p.,2 Fig., submitted to Physica C (M2S-Rio proceedings); v2: 1 ref
adde
Nonmagnetic impurity effects in MgB
We study nonmagnetic impurity effects in MgB using the quasiclassical
equations of superconductivity for a weak-coupling two-band model. Parameters
in the model are fixed so as to reproduce experiments on MgB as closely
as possible. The quasiparticle density of states and the specific heat are
calculated for various values of the interband impurity scattering. The density
of states changes gradually from a two-gap structure into the conventional
single-gap structure as the interband scattering increases. It is found that
the excitation threshold is not a monotonic function of the interband
scattering. Calculated results for the specific heat are in good agreements
with experiments on samples after irradiation
Transition Spectra for a BCS Superconductor with Multiple Gaps: Model Calculations for MgB_2
We analyze the qualitative features in the transition spectra of a model
superconductor with multiple energy gaps, using a simple extension of the
Mattis-Bardeen expression for probes with case I and case II coherence factors.
At temperature T = 0, the far infrared absorption edge is, as expected,
determined by the smallest gap. However, the large thermal background may mask
this edge at finite temperatures and instead the secondary absorption edges
found at Delta_i+Delta_j may become most prominent. At finite T, if certain
interband matrix elements are large, there may also be absorption peaks at the
gap difference frequencies | Delta_i-Delta_j | . We discuss the effect of
sample quality on the measured spectra and the possible relation of these
predictions to the recent infrared absorption measurement on MgB_2
Noether symmetries for two-dimensional charged particle motion
We find the Noether point symmetries for non-relativistic two-dimensional
charged particle motion. These symmetries are composed of a quasi-invariance
transformation, a time-dependent rotation and a time-dependent spatial
translation. The associated electromagnetic field satisfy a system of
first-order linear partial differential equations. This system is solved
exactly, yielding three classes of electromagnetic fields compatible with
Noether point symmetries. The corresponding Noether invariants are derived and
interpreted
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