1,728 research outputs found
Study of the topological Hall effect on simple models
Recently, a chirality-driven contribution to the anomalous Hall effect has
been found that is induced by the Berry phase and does not directly involve
spin-orbit coupling. In this paper, we will investigate this effect numerically
in a two-dimensional electron gas with a simple magnetic texture model. Both
the adiabatic and non-adiabatic regimes are studied, including the effect of
disorder. By studying the transition between both regimes the discussion about
the correct adiabaticity criterium in the diffusive limit is clarified.Comment: 8 pages, 7 figures, revtex
Measuring carrier density in parallel conduction layers of quantum Hall systems
An experimental analysis for two parallel conducting layers determines the
full resistivity tensor of the parallel layer, at magnetic fields where the
other layer is in the quantum Hall regime. In heterostructures which exhibit
parallel conduction in the modulation-doped layer, this analysis quantitatively
determines the charge density in the doping layer and can be used to estimate
the mobility. To illustrate one application, experimental data show magnetic
freeze-out of parallel conduction in a modulation doped heterojunction. As
another example, the carrier density of a minimally populated second subband in
a two-subband quantum well is determined. A simple formula is derived that can
estimate the carrier density in a highly resistive parallel layer from a single
Hall measurement of the total system.Comment: 7 pages, 7 figure
Single-valley high-mobility (110) AlAs quantum wells with anisotropic mass
We studied a doping series of (110)-oriented AlAs quantum wells (QWs) and
observed transport evidence of single anisotropic-mass valley occupancy for the
electrons in a 150 \AA wide QW. Our calculations of strain and quantum
confinement for these samples predict single anisotropic-mass valley occupancy
for well widths greater than 53 \AA. Below this, double-valley occupation
is predicted such that the longitudinal mass axes are collinear. We observed
mobility anisotropy in the electronic transport along the crystallographic
directions in the ratio of 2.8, attributed to the mass anisotropy as well as
anisotropic scattering of the electrons in the X-valley of AlAs
Mesoscopic magnetoelectric effect in chaotic quantum dots
The magnitude of the inverse Faraday effect (IFE), a static magnetization due
to an ac electric field, can be strongly increased in a mesoscopic sample,
sensitive to time-reversal symmetry (TRS) breaking. Random rectification of ac
voltages leads to a magnetization flux, which can be detected by an asymmetry
of Hall resistances in a multi-terminal setup. In the absence of applied
magnetic field through a chaotic quantum dot the IFE scale, quadratic in
voltage, is found as an analytic function of the ac frequency, screening, and
coupling to the contacts and floating probes, and numerically it does not show
any effect of spin-orbit interaction. Our results qualitatively agree with a
recent experiment on TRS-breaking in a six-terminal Hall cross.Comment: 4+ pages, 2 figures; v2-published version, small change
X-ray photoemission characterization of La_{0.67}(Ca_{x}Sr_{1-x})_{0.33}MnO_{3} films
The Curie temperature and x-ray photoemission spectra of thin films of
La_{0.67}(Ca_{x}Sr_{1-x})_{0.33}MnO_{3} (LCSMO) have been studied as a function
of the Ca/Sr ratio. The films were grown by off-axis cosputtering from
individual targets of La_{0.67}Ca_{0.33}MnO_{3} (LCMO) and
La_{0.67}Sr_{0.33}MnO_{3} (LSMO) onto (100) oriented NdGaO_{3} substrates. The
films grow with a (100) orientation, with no other orientations observed by
x-ray diffraction. For the alloy mixtures, the Curie temperature, T_C, varies
slowly as the Ca/Sr is decreased, remaining 300 K, while for the LCMO
and LSMO films T_C is 260 and 330 K, respectively. The Mn-O valence structure
is composed of two dominant peaks, whose positions undergo a change as the Ca
fraction is decreased. The core lines behave as linear combinations of lines
from pure LCMO and LSMO.Comment: 3 pages, 5 eps figures. To be published in Journal of Applied Physics
(Proceedings of MMM'98
Different effects of Ni and Co substitution on the transport properties of BaFe2As2
We report resistivity and Hall effect results on Ba(Fe1-xNix)2As2 and compare
them with those in Ba(Fe1-xCox)2As2. The Hall number RH is negative for all x
values from 0.01 to 0.14, which indicates that electron carriers dominate the
transport both in the magnetic and paramagnetic regime. We analyse the data in
the framework of a two-band model. Without any assumption on the number of
carriers, we show that the electron resistivity can be estimated with good
accuracy in the low temperature paramagnetic range. Although the phase diagrams
of the two families are very similar with respect to the extra electrons added
in the system, we find that the transport properties differ in several aspects.
First, we evidence that the contribution of holes to the transport is more
important for Ni doping than for Co doping. Secondly, Ni behaves as a stronger
scatterer for the electrons, as the increase of the residual electron
resistivity rho/x is about four times larger for Ni than for Co in the most
doped samples.Comment: 8 pages, 8 figure
Hole and Electron Contributions to the Transport Properties of Ba(Fe_(1-x)Ru_x)_2As_2 Single Crystals
We report a systematic study of structural and transport properties in single
crystals of Ba(Fe_(1-x)Ru_x)_2As_2 for x ranging from 0 to 0.5. The isovalent
substitution of Fe by Ru leads to an increase of the a parameter and a decrease
of the c parameter, resulting in a strong increase of the AsFeAs angle and a
decrease of the As height above the Fe planes. Upon Ru substitution, the
magnetic order is progressively suppressed and superconductivity emerges for x
> 0.15, with an optimal Tc ~ 20K at x = 0.35 and coexistence of magnetism and
superconductivity between these two Ru contents. Moreover, the Hall coefficient
RH which is always negative and decreases with temperature in BaFe2As2, is
found to increase here with decreasing T and even change sign for x > 0.15. For
x_Ru = 0.35, photo-emission studies have shown that the number of holes and
electrons are similar with n_e = n_h ~ 0.11, that is twice larger than found in
BaFe2As2 [1]. Using this estimate, we find that the transport properties of
Ba(Fe_0.65Ru_0.35)_2As_2 can be accounted for by the conventional multiband
description for a compensated semi-metal. In particular, our results show that
the mobility of holes is strongly enhanced upon Ru addition and overcomes that
of electrons at low temperature when x_Ru > 0.15.Comment: new version with minor correction
Financing Measures to Avert, Minimise and Address Loss and Damage: Options for the Green Climate Fund (GCF)
This report was prepared with financial support from the German Federal Ministry of Economic Cooperation and Development (BMZ). We are grateful to the written comments and suggestions provided by Olivia Serdeczny (Climate Analytics) and Andrea Iro (GCF Secretariat). This report benefitted from the input by Raju Chhetri (PRC), Zoha Shawoo (SEI) and others during discussions with the Working Group on Financing Loss and Damage on 13 May 2020. It further benefitted from the input by Mariya Aleksandrova (DIE), Jean-Paul Brice Affana (Germanwatch), Rebecca Carter (WRI), Stephane Hallegatte (World Bank), Tessa Kelly (IFRC), Sönke Kreft (MCII), Erling Kverevik (Directorate for Civil Protection, Norway), Donna Mitzi Lagdameo (IFRC), Nicolina Lamhauge (OECD), Reinhard Mechler (IIASA), Jelena Milos (EU Commission), Le-Anne Roper (Ministry of Economic Growth and Job Creation, Jamaica), Sarah Zügel (Federal Ministry for Environment, Nature Conservation and Nuclear Safety), Christoph von Stechow (BMZ) and Sebastian Forsch (BMZ) during discussions at an Expert Roundtable on 24 June 2020.1 Introduction 2 Background: loss and damage in the UNFCCC negotiations 3 Background: research on loss and damage 3.1. Conceptualisation and framing of Loss & Damage 3.2. The Costs of Loss & Damage 3.3. Financing Loss & Damage 4 Loss and Damage and the GCF 4.1. Framework conditions to finance action on loss and damage under the GCF Governing Instrument Strategic Plan Results Management Framework Investment Criteria 4.2. Current funding for action on loss and damage under the GCF Occurrence of L&D-related terminology WIM ExCom’s workstreams and the GCF portfolio 5 Discussion and Conclusion 5.1. Range of policy options 5.2. Recommendations References Annex 1: The Warsaw International Mechanism for Loss and Damage Annex 2: An Overview of Investment Support Instruments Relevant for L&D Annex 3. Extent to which the GCF investment criteria’s indicative assessment factors are relevant for the WIM ExCom Workstreams Annex 4. Methods used for section 4.
Characterization of transport and magnetic properties in thin film La(0.67)(Ca(x)Sr(1-x))(0.33)MnO(3) mixtures
We have grown thin films of (100) oriented
La_{0.67}(Ca_{x}Sr_{1-x})_{0.33}MnO_{3} on (100) NdGaO_{3} substrates by
off-axis sputtering. We have looked at the changes in the resistivity and
magnetoresistance of the samples as the Ca/Sr ratio was varied. We find that as
the calcium fraction is decreased, the lattice match to the substrate
decreases, and the films become more disordered, as observed in transport
measurements and the variation in Curie and peak resistance temperatures. We
find a correlation between the temperature independent and T^2 terms to the low
temperature resistivity. The room temperature magnetoresistance exhibits a
maximum as the peak temperature is increased by the substitution of Sr for Ca,
and a change in the field dependence to the resistivity at room temperature is
observed.Comment: 5 pages, 6 eps figures, to be published in Journal of Applied Physic
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