2,801 research outputs found
A simple microscopic model for the dynamics of adhesive failure
We consider a microscopic model for the failure of soft adhesives in tension
based on ideas of bond rupture under dynamic loading. Focusing on adhesive
failure under loading at constant velocity, we demonstrate that bi-modal curves
of stress against strain may occur due to effects of finite polymer chain or
bond length and characterise the loading conditions under which such bi-modal
behaviour is observed. The results of this analysis are in qualitative
agreement with experiments performed on unconfined adhesives in which failure
does not occur by cavitation.Comment: 11 pages, 5 figure
Spin, charge and orbital ordering in La0.5Sr1.5MnO4
We have analyzed the experimental evidence of charge and orbital ordering in
La0.5Sr1.5MnO4 using first principles band structure calculations. Our results
suggest the presence of two types of Mn sites in the system. One of the Mn
sites behaves like an Mn(3+) ion, favoring a Jahn-Teller distortion of the
surrounding oxygen atoms, while the distortion around the other is not a simple
breathing mode kind. Band structure effects are found to dominate the
experimental spectrum for orbital and charge ordering, providing an alternate
explanation for the experimentally observed results.Comment: 4 pages + 3 figures; To appear in Phys. Rev. Let
Electronic Structure of Sr_2FeMoO_6
We have analysed the unusual electronic structure of Sr_2FeMoO_6 combining
ab-initio and model Hamiltonian approaches. Our results indicate that there are
strong enhancements of the intraatomic exchange strength at the Mo site as well
as the antiferromagnetic coupling strength between Fe and Mo sites. We discuss
the possibility of a negative effective Coulomb correlation strength (U_{eff})
at the Mo site due to these renormalised interaction strengths.Comment: To appear in Phys. Rev. Let
Understanding the bulk electronic structure of Ca1-xSrxVO3
We investigate the electronic structure of Ca1-xSrxVO3 using careful
state-of-the-art experiments and calculations. Photoemission spectra using
synchrotron radiation reveal a hitherto unnoticed polarization dependence of
the photoemission matrix elements for the surface component leading to a
substantial suppression of its intensity. Bulk spectra extracted with the help
of experimentally determined electron escape depth and estimated suppression of
surface contributions resolve outstanding puzzles concerning the electronic
structure in Ca1-xSrxVO3.Comment: 4 pages including 3 figure
Ultra-narrow and widely tunable Mn^(2+) Emission from Single Nanocrystals of ZnS-CdS alloy
Extensively studied Mn-doped semiconductor nanocrystals have invariably
exhibited photoluminescence (PL) over a narrow energy window of width <= 149
meV in the orange-red region and a surprisingly large spectral width (>= 180
meV), contrary to its presumed atomic-like origin. Carrying out emission
measurements on individual single nanocrystals and supported by ab initio
calculations, we show that Mn PL emission, in fact, can (i) vary over a much
wider range (~ 370 meV) covering the deep green-deep red region and (ii)
exhibit widths substantially lower (~ 60-75 meV) than reported so far, opening
newer application possibilities and requiring a fundamental shift in our
perception of the emission from Mn-doped semiconductor nanocrystals.Comment: 5 pages, 5 figure
Elasticity of an interfacial particle raft
We study the collective behaviour of a close packed monolayer of non-Brownian
particles at a fluid-liquid interface. Such a particle raft forms a
two-dimensional elastic solid and can support anisotropic stresses and strains,
e.g. it buckles in uniaxial compression and cracks in tension. We characterise
this solid in terms of a Young's modulus and Poisson ratio derived from simple
theoretical considerations and show the validity of these estimates by using an
experimental buckling assay to deduce the Young's modulus.Comment: 7 pages, 5 figure
Unusual directional dependence of exchange energies in GaAs diluted with Mn: is the RKKY description relevant?
Ferromagnetism in Mn-doped GaAs, the prototypical dilute magnetic semiconductor (DMS), has so far been attributed to hole mediated RKKY-type interactions. First-principles calculations reveal a strong direction dependence of the ferromagnetic (FM) stabilization energy for Mn pairs, a dependence that cannot be explained within RKKY. In the limit of a hostlike hole engineered here where the RKKY model is applicable, the exchange energies are strongly reduced, suggesting that this limit cannot explain the observed ferromagnetism. The dominant contribution stabilizing the FM state is found to be maximal for <110 >-oriented Mn pairs and minimal for < 100 >-oriented Mn pairs, providing an alternate explanation for magnetism in such materials in terms of energy lowering due to p-d hopping interactions, and offering a new design degree of freedom to enhance FM
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