151 research outputs found
CrO2: a self-doped double exchange ferromagnet
Band structure calculations of CrO2 carried out in the LSDA+U approach reveal
a clear picture of the physics behind the metallic ferromagnetic properties.
Arguments are presented that the metallic ferromagnetic oxide CrO2 belongs to a
class of materials in which magnetic ordering exists due to double exchange (in
this respect CrO2 turns out to be similar to the CMR manganates). It is
concluded that CrO2 has small or even negative charge transfer gap which can
result in self-doping. Certain experiments to check the proposed picture are
suggested.Comment: 4 pages, 4 Figure
Large two-level magnetoresistance effect in doped manganite grain boundary junctions
We performed a systematic analysis of the tunneling magnetoresistance (TMR)
effect in single grain boundary junctions formed in epitaxial
La(2/3)Ca(1/3)MnO(3) films deposited on SrTiO(3) bicrystals. For magnetic
fields H applied parallel to the grain boundary barrier, an ideal two-level
resistance switching behavior with sharp transitions is observed with a TMR
effect of up to 300% at 4.2 K and still above 100% at 77 K. Varying the angle
between H and the grain boundary results in differently shaped resistance vs H
curves. The observed behavior is explained within a model of magnetic domain
pinning at the grain boundary interface.Comment: 4 pages, 3 figures, to appear in Phys. Rev. B (Rapid Comm.
Basic obstacle for electrical spin-injection from a ferromagnetic metal into a diffusive semiconductor
We have calculated the spin-polarization effects of a current in a two
dimensional electron gas which is contacted by two ferromagnetic metals. In the
purely diffusive regime, the current may indeed be spin-polarized. However, for
a typical device geometry the degree of spin-polarization of the current is
limited to less than 0.1%, only. The change in device resistance for parallel
and antiparallel magnetization of the contacts is up to quadratically smaller,
and will thus be difficult to detect.Comment: Revtex, 4 pages, 3 figures (eps), Definition of spin pilarization
changed to standard definition in GMR, some straight forward algebra removed.
To appear as PRB Rap. Comm. August 15t
Single Spin Superconductivity: Formulation and Ginzburg-Landau Theory
We describe a novel superconducting phase that arises due to a pairing
instability of the half-metallic antiferromagnetic (HM AFM) normal state. This
single spin superconducting (SSS) phase contains broken time reversal symmetry
in addition to broken gauge symmetry, the former due to the underlying magnetic
order in the normal state. A classification of normal state symmetries leads to
the conclusion that the HM AFM normal phase whose point group contains the
inversion operator contains the least symmetry possible which still allows for
a zero momentum pairing instability. The Ginzburg-Landau free energy for the
superconducting order parameter is constructed consistent with the symmetry of
the normal phase, electromagnetic gauge invariance and the crystallographic
point group symmetry including inversion. For cubic, hexagonal and tetragonal
point groups, the possible symmetries of the superconducting phase are
classified, and the free energy is used to construct a generalized phase
diagram. We identify the leading candidate out of the possible SSS phases for
each point group. The symmetry of the superconducting phase is used to
determine the cases where the gap function has generic zeros (point or line
nodes) on the Fermi surface. Such nodes always occur, hence thermodynamic
properties will have power-law behavior at low temperature.Comment: 39 pages, RevTeX, 4 PostScript figures included, submitted to Phys.
Rev.
A Novel High-Affinity Sucrose Transporter Is Required for Virulence of the Plant Pathogen Ustilago maydis
A novel, high-affinity sucrose transporter identified in the plasma membrane of the plant pathogen Ustilago maydis is essential for fungal virulence and successful infection of maize
First principles electronic structure of spinel LiCr2O4: A possible half-metal?
We have employed first-principles electronic structure calculations to
examine the hypothetical (but plausible) oxide spinel, LiCr2O4 with the d^{2.5}
electronic configuration. The cell (cubic) and internal (oxygen position)
structural parameters have been obtained for this compound through structural
relaxation in the first-principles framework. Within the one-electron band
picture, we find that LiCr2O4 is magnetic, and a candidate half-metal. The
electronic structure is substantially different from the closely related and
well known rutile half-metal CrO2. In particular, we find a smaller conduction
band width in the spinel compound, perhaps as a result of the distinct topology
of the spinel crystal structure, and the reduced oxidation state. The magnetism
and half-metallicity of LiCr2O4 has been mapped in the parameter space of its
cubic crystal structure. Comparisons with superconducting LiTi2O4 (d^{0.5}),
heavy-fermion LiV2O4 (d^{1.5}) and charge-ordering LiMn2O4 (d^{3.5}) suggest
the effectiveness of a nearly-rigid band picture involving simple shifts of the
position of E_F in these very different materials. Comparisons are also made
with the electronic structure of ZnV2O4 (d^{2}), a correlated insulator that
undergoes a structural and antiferromagnetic phase transition.Comment: 9 pages, 7 Figures, version as published in PR
Towards Open Access Publishing in High Energy Physics : Report of the SCOAP3 Working Party
This Report concerns the implementation of a process today supported by leading actors from the particle physics community, and worked through in detail by members of an international Working Party. The initiative offers an opportunity for the cost-effective dissemination of high-quality research articles in particle physics, enabling use of the new technologies of e-Science across the literature of High Energy physics
Absence of repellents in Ustilago maydis induces genes encoding small secreted proteins
The rep1 gene of the maize pathogen Ustilago maydis encodes a pre-pro-protein that is processed in the secretory pathway into 11 peptides. These so-called repellents form amphipathic amyloid fibrils at the surface of aerial hyphae. A SG200 strain in which the rep1 gene is inactivated (∆rep1 strain) is affected in aerial hyphae formation. We here assessed changes in global gene expression as a consequence of the inactivation of the rep1 gene. Microarray analysis revealed that only 31 genes in the ∆rep1 SG200 strain had a fold change in expression of ≥2. Twenty-two of these genes were up-regulated and half of them encode small secreted proteins (SSPs) with unknown functions. Seven of the SSP genes and two other genes that are over-expressed in the ∆rep1 SG200 strain encode proteins that can be classified as secreted cysteine-rich proteins (SCRPs). Interestingly, most of the SCRPs are predicted to form amyloids. The SCRP gene um00792 showed the highest up-regulation in the ∆rep1 strain. Using GFP as a reporter, it was shown that this gene is over-expressed in the layer of hyphae at the medium-air interface. Taken together, it is concluded that inactivation of rep1 hardly affects the expression profile of U. maydis, despite the fact that the mutant strain has a strong reduced ability to form aerial hyphae
Pandemic gardening:A narrative review, vignettes and implications for future research
There is a significant amount of evidence highlighting the health, wellbeing and social benefits of gardening during previous periods of crises. These benefits were also evident during the COVID-19 pandemic. This paper presents a narrative review exploring gardening during the early stages of the COVID-19 pandemic to understand the different forms of gardening that took place during this crisis and key elements of this activity. Research about gardening during the pandemic focused on food (in)security and disrupted food systems, the health and wellbeing benefits of gardening, and the social dimensions of gardening. We offer three vignettes of our own research to highlight key insights from local, national and international perspectives of gardening during the pandemic. The paper's conclusion outlines how researchers, policy makers and public health practitioners can harness what has been learned from gardening during the pandemic to ensure these benefits are more widely available and do not exacerbate already entrenched health inequalities in society.</p
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