2,865 research outputs found
Asymmetric field dependence of magnetoresistance in magnetic films
We study an asymmetric in field magnetoresistance that is frequently observed
in magnetic films and, in particular, the odd longitudinal voltage peaks that
appear during magnetization reversal in ferromagnetic films, with out-of-plane
magnetic anisotropy. We argue that the anomalous signals result from small
variation of magnetization and Hall resistivity along the sample. Experimental
data can be well described by a simple circuit model, the latter being
supported by analytic and numerical calculations of current and electric field
distribution in films with a gradual variation of the magnetization and Hall
resistance.Comment: 7 pages, 5 figures, to be published in Phys. Rev.
Unconventional Anomalous Hall Effect in the Metallic Triangular-Lattice Magnet PdCrO2
We experimentally reveal an unconventional anomalous Hall effect (UAHE) in a
quasi-two-dimensional triangular-lattice antiferromagnet PdCrO2. Using high
quality single crystals of PdCrO2, we found that the Hall resistivity deviates
from the conventional behavior below T* = 20 K, noticeably lower than TN = 37.5
K, at which Cr^{3+} (S=3/2) spins order in a 120 degree structure. In view of
the theoretical expectation that the spin chirality cancels out in the simplest
120 degree spin structure, we discuss required conditions for the emergence of
UAHE within Berry-phase mechanisms.Comment: 4 pages, 5 figures, accepted for publication in PR
Superconducting d-wave junctions: The disappearance of the odd ac components
We study voltage-biased superconducting planar d-wave junctions for arbitrary
transmission and arbitrary orientation of the order parameters of the
superconductors. For a certain orientation of the superconductors the odd ac
components disappear, resulting in a doubling of the Josephson frequency. We
study the sensitivity of this disappearance to orientation and compare with
experiments on grain boundary junctions. We also discuss the possibility of a
current flow parallel to the junction.Comment: 5 pages, 3 figure
Tunneling spectra for ()-wave superconductors versus tunneling spectra for ()-wave superconductors
The tunneling conductance spectra of a normal metal / insulator / singlet
superconductor is calculated from the reflection amplitudes using the
Blonder-Tinkham-Klapwijk (BTK) formulation. The pairing symmetry of the
superconductor is assumed to be , or . It
is found that in the ()-wave case there is a well defined
conductance peak in the conductance spectra, in the amplitude of the secondary
s-wave component. In the ()-wave case the tunneling
conductance has residual values within the gap, due to the formation of bound
states. The bound state energies depend on the angle of the incident
quasiparticles, and also on the boundary orientation. On the basis of this
observation an electron focusing experiment is proposed to probe the
()-wave state.Comment: 17 pages with 9 figure
Intrinsic vs. extrinsic anomalous Hall effect in ferromagnets
A unified theory of the anomalous Hall effect (AHE) is presented for
multi-band ferromagnetic metallic systems with dilute impurities. In the clean
limit, the AHE is mostly due to the extrinsic skew-scattering. When the Fermi
level is located around anti-crossing of band dispersions split by spin-orbit
interaction, the intrinsic AHE to be calculated ab initio is resonantly
enhanced by its non-perturbative nature, revealing the extrinsic-to-intrinsic
crossover which occurs when the relaxation rate is comparable to the spin-orbit
interaction energy.Comment: 5 pages including 4 figures, RevTex; minor changes, to appaer in
Phys. Rev. Let
Topological Hall effect and Berry phase in magnetic nanostructures
We discuss the anomalous Hall effect in a two-dimensional electron gas
subject to a spatially varying magnetization. This topological Hall effect
(THE) does not require any spin-orbit coupling, and arises solely from Berry
phase acquired by an electron moving in a smoothly varying magnetization. We
propose an experiment with a structure containing 2D electrons or holes of
diluted magnetic semiconductor subject to the stray field of a lattice of
magnetic nanocylinders. The striking behavior predicted for such a system (of
which all relevant parameters are well known) allows to observe unambiguously
the THE and to distinguish it from other mechanisms.Comment: 5 pages with 4 figure
Resonant tunneling through a small quantum dot coupled to superconducting leads
We address the problem of non-linear transport through discrete electronic
levels in a small quantum dot coupled to superconducting electrodes. In our
approach the low temperature I-V characteristics can be calculated including
all multiple quasi-particle and Andreev processes. The limit of very weak
coupling to the leads and large charging energies is briefly analyzed comparing
the calculated lineshapes of the I-V curves with recent experimental results.
When the coupling to the leads increases and Coulomb blockade effects can be
neglected, the combination of multiple Andreev processes and resonant
transmission gives rise to a rich subgap structure which largely differs from
the one found in the more studied S-N-S systems. We show how multiple processes
can be included within a simple sequential tunneling picture qualitatively
explaining the subgap structure. We suggest an experimental set-up where the
predicted effects could be observed.Comment: 11 pages, 4 postscript figures, to be published in Phys. Rev. B
(rapid communications
Berry's phase contribution to the anomalous Hall effect of gadolinium
When conduction electrons are forced to follow the local spin texture, the
resulting Berry phase can induce an anomalous Hall effect (AHE). In gadolinium,
as in double-exchange magnets, the exchange interaction is mediated by the
conduction electrons and the AHE may therefore resemble that of chromium
dioxide and other metallic double-exchange ferromagnets. The Hall resistivity,
magnetoresistance, and magnetization of single crystal gadolinium were measured
in fields up to 30 T. Measurements between 2 K and 400 K are consistent with
previously reported data. A scaling analysis for the Hall resistivity as a
function of the magnetization suggests the presence of a Berry's-phase
contribution to the anomalous Hall effect.Comment: 6 pages, 7 figures, submitted to Phys. Rev.
Orbital magnetization and its effects in spin-chiral ferromagnetic Kagome lattice
Recently, Berry phase in the semiclassical dynamical of Bloch electrons has
been found to make a correction to the phase-space density of states and a
general multi-band formula for finite-temperature orbital magnetization has
been given [Phys. Rev. Lett. \textbf{97}, 026603 (2006)], where the orbital
magnetization consists of two parts, i.e., the conventional part
and the Berry-phase correction part . Using this general
formula, we theoretically investigate the orbital magnetization and its effects
on thermoelectric transport and magnetic susceptibility properties of the
two-dimensional \textit{kagom\'{e}} lattice with spin anisotropies included.
The study in this paper is highly interesting by the occurrence of nonzero
Chern number in the lattice. The spin chirality parameter (see text)
results in profound effects on the orbital magnetization properties. It is
found that the two parts in orbital magnetization opposite each other. In
particular, we show that and yield the paramagnetic and
diamagnetic responses, respectively. It is further shown that the orbital
magnetization displays fully different behavior in the metallic and insulating
regions, which is due to the different roles and play in
these two regions. The anomalous Nernst conductivity is also calculated, which
displays a peak-valley structure as a function of the electron Fermi energy.Comment: 9 pages, 7 figure
A precursor state to unconventional superconductivity in CeIrIn
We present sensitive measurements of the Hall effect and magnetoresistance in
CeIrIn down to temperatures of 50 mK and magnetic fields up to 15 T. The
presence of a low temperature coherent Kondo state is established. Deviations
from Kohler's rule and a quadratic temperature dependence of the cotangent of
the Hall angle are reminiscent of properties observed in the high temperature
superconducting cuprates. The most striking observation pertains to the
presence of a \textit{precursor} state--characterized by a change in the Hall
mobility--that appears to precede the superconductivity in this material, in
similarity to the pseudogap in the cuprate high superconductors.Comment: 4 figure
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