925 research outputs found
Continuous melting of a driven two-dimensional flux lattice with strong pins
The phase diagram of a driven two-dimensional vortex lattice in the presence
of dense quasi-point pins is investigated. The transition from the crystal to
the liquid is found continuous at intermediate inductions. The correlations in
the pseudo random force that allow for an uncomplete unbinding of the
dislocations is proposed as a key mechanism to account for the continuous
transition.Comment: 7 pages, 8 figure
Transition to plastic motion as a critical phenomenon and anomalous interface layer of a 2D driven vortex lattice
The dynamic transition between the ordered flow and the plastic flow is
studied for a two-dimensional driven vortex lattice, in the presence of sharp
and dense pinning centers, from numerical simulations. For this system, which
does not show smectic ordering, the lattice exhibits a first order transition
from a crystal to a liquid, shortly followed by the dynamical transition to the
plastic flow. The resistivity provides a critical order parameter for the
latter, and critical exponents are determined in analogy with a percolation
transition. At the boundary between a pinned region and an unpinned one, an
anomalous layer is observed, where the vortices are more strongly pinned than
in the bulk.Comment: 7 pages, 7 figure
Magnetic critical properties and basal-plane anisotropy of SrIrO
The anisotropic magnetic properties of SrIrO are investigated, using
longitudinal and torque magnetometry. The critical scaling across of the
longitudinal magnetization is the one expected for the 2D XY universality
class. Modeling the torque for a magnetic field in the basal-plane, and taking
into account all in-plane and out-of-plane magnetic couplings, we derive the
effective 4-fold anisotropy 1 10 erg mole. Although
larger than for the cuprates, it is found too small to account for a
significant departure from the isotropic 2D XY model. The in-plane torque also
allows us to put an upper bound for the anisotropy of a field-induced shift of
the antiferromagnetic ordering temperature
Ordering in Heisenberg Spin Glasses
For five different Heisenberg spin glass systems, torque experiments were
performed in applied magnetic fields up to . The Dzyaloshinski-Moriya
random anisotropy strengths, the in-field torque onset temperatures, and the
torque relaxation were measured. Critical exponents were estimated
independently using a standard protocol. The data are strong evidence for a
true spin glass ordered state which survives under high applied magnetic
fields; they can be interpreted consistently in terms of a chiral ordering
model with replica symmetry breaking as proposed by Kawamura and coworkers.Comment: 4 pages 4 figures. Revised version accepted by PR
Anisotropy and interaction effects of strongly strained SrIrO3 thin films
Magneto-transport properties of SrIrO thin films epitaxially grown on
SrTiO, using reactive RF sputtering, are investigated. A large anisotropy
between the in-plane and the out-of-plane resistivities is found, as well as a
signature of the substrate cubic to tetragonal transition. Both observations
result from the structural distortion associated to the epitaxial strain. The
low-temperature and field dependences of the Hall number are interpreted as due
to the contribution of Coulomb interactions to weak localization, evidencing
the strong correlations in this material. The introduction of a contribution
from magnetic scatters, in the analysis of magnetoconductance in the weakly
localized regime, is proposed as an alternative to an anomalously large
temperature dependence of the Land\'{e} coefficient
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
Anisotropy of the in-plane angular magnetoresistance of electron-doed Sr1-xLaxCuO2 thin films
Signatures of antiferromagnetism (AF) in the underdoped Ln2-xCexCuO4 (Ln =
Nd, Pr,...) family are observed even for doping levels for which
superconductivity exists. We have looked for a similar property in a different
electron-doped cuprate family, Sr1-xLaxCuO2, which consists of CuO2 planes
separated by Sr/La atoms, and is exempt of the possible influence of magnetic
rare earth ions. We report in-plane magnetoresistance measurements in the
normal state of underdoped, superconducting, c-axis oriented, epitaxial
Sr1-xLaxCuO2 thin films. This probe is sensitive to spin arrangement and we
find that the in-plane magnetoresistance, which is negative and does not
saturate for T, exhibits an angular dependence when measured upon rotating a
magnetic field within the CuO2 planes. The analysis reveals a superposition of
fourfold and twofold angular oscillations. Both of these increase in amplitude
with increasing field and decreasing and appear below a temperature, which gets
higher with decreasing doping levels. Our results demonstrate that these
magnetoresistance oscillations, also observed for the Ln2-xCexCuO4 (Ln = Nd,
Pr,...) family and attributed to an AF signature, are, without ambiguity, a
property of CuO2 planes. Besides, these oscillations vary with doping in an
unusual way compared to previous results: fourfold oscillations are essentially
present in the more underdoped samples while only twofold oscillations are
visible in the less underdoped ones. This intriguing observation appears to be
a consequence of spin dilution with increasing doping level.Comment: 25 pages, 6 figure
Non linear transport properties of an insulating YBCO nano-bridge
We have investigated the transport properties of an insulating
sub-micrometric YBa2Cu3O7-d bridge, patterned on a thin film. As expected for a
variable-range-hopping insulator, transport is found non linear. The reduced
dimension allows for the observation of an individual fluctuator generating
random telegraph noise, which dynamics could be explored as a function of the
temperature and transport current. Some recordings clearly exhibit three levels
fluctuating resistance, with comparable level separation and correlated
dynamics, which likely result from the existence of two states or correlated
clustered charge traps
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
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