1,712 research outputs found
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
Analysis of macrobenthic communities in Flanders, Belgium, using a stepwise input variable selection procedure with artificial neural networks
A malachite sunbird pollination guild in the Cape flora, with implications for the endangered Brunsvigia litoralis
Développement de méthodes d'analyse des hydrocarbures et micro-polluants organiques dans le milieu marin: Programme S.S.T.C. "Gestion durable de la Mer du Nord": Rapport Final
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
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
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
Conditional nationally determined contributions in the Paris Agreement: foothold for equity or Achilles heel?
The Paris Agreement’s success depends on parties’ implementation of their Nationally Determined Contributions (NDCs) towards the Paris Agreement’s goals. In these climate action plans, most developing countries make their mitigation and adaptation contributions conditional upon receiving international support (finance, technology transfer and/or capacity building). While provision of support for NDC implementation could enhance equity among countries, the feasibility of NDC implementation might be challenged by the large number of conditional NDCs. This paper addresses the implications of this tension based on an analysis of all 168 NDCs. We find that feasibility is challenged because conditions applied to NDCs are often not well defined. Moreover, the costs of implementing all conditional contributions are too high to be covered by existing promises of support from developed countries, even if the entire annual $100 billion of climate finance were earmarked for NDC implementation. Consistent with principles of equity and the prioritization in the Paris Agreement, a higher proportion of Least Developed Countries (LDCs) and Small Island Developing States (SIDS) have conditional NDCs than do other countries. However, differences between the distribution of countries requesting support and those currently receiving support, in particular among middle-income countries, demonstrates potential tensions between feasibility and equity. The article concludes with recommendations on how cost estimates and updated NDCs can be strengthened to ensure support for NDC implementation is targeted more equitably and cost-effectively. Key policy insights -Support requested by developing countries to implement conditional NDCs far exceeds existing funding pledges. -Differences between existing patterns of financial assistance, and those implied by requests under conditional NDCs, mean that supporting NDCs may require a significant shift in provider countries’ priorities for allocating climate finance. This may challenge feasibility. -The Paris Agreement’s provisions on prioritizing LDCs and SIDS offer valuable guidance in making difficult choices on allocating support. -To increase the likelihood of attracting support, developing countries (assisted by capacity building as needed), should include credible cost estimates in future NDCs and formulate investment plans. -By outlining plans to mobilize support in their NDCs, developed countries can reassure developing countries that raising the ambition of NDCs is feasibl
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