We employ dynamical mean-field theory to study the optical conductivity
σ
(
ω
)
of one hole in the Holstein-
t–
J model. We provide an exact solution for
σ
(
ω
)
in the limit of infinite ...connectivity. We apply our analysis to
Nd
2
-
x
Ce
x
CuO
4
. We show that our model can explain many features of the optical conductivity in this compounds in terms of magnetic/lattice polaron formation.
We propose an intrinsic spin scattering mechanism in graphene originated by the interplay of atomic spin-orbit interaction and the local curvature induced by flexural distortions of the atomic ...lattice. Starting from a multiorbital tight-binding Hamiltonian with spin-orbit coupling considered nonperturbatively, we derive an effective Hamiltonian for the spin scattering of the Dirac electrons due to flexural distortions. We compute the spin lifetime due to both flexural phonons and ripples and we find values in the microsecond range at room temperature. Interestingly, this mechanism is anisotropic on two counts. First, the relaxation rate is different for off-plane and in-plane spin quantization axis. Second, the spin relaxation rate depends on the angle formed by the crystal momentum with the carbon-carbon bond. In addition, the spin lifetime is also valley dependent. The proposed mechanism sets an upper limit for spin lifetimes in graphene and will be relevant when samples of high quality can be fabricated free of extrinsic sources of spin relaxation.
The mangrove snail Cerithidea decollata feeds on the ground at low water, and about two hours before high water climbs Avicennia marina trunks settling 20–40 cm above the level that the incoming tide ...will reach. The moment that C. decollata must start to measure the vertical distance it has to creep up the trunk to avoid submersion corresponds to the point at which creeping switches from a horizontal to vertical movement (the “0” point). Two vertical movements interrupted by a short horizontal movement were added together; however, if the horizontal interruption was wider than 10 cm a new “0” point was set, and snails climbed higher than control snails, according to the level of the horizontal interruption, without adding the two vertical segments. Through forcing snails to both climb and descend, we observed that they do not appear to be capable of subtraction.
The role of the multiorbital effects on the emergence of frustrated electronic orders on the triangular lattice at half filling is investigated through an extended spinless fermion Hubbard model. By ...using two complementary approaches, unrestricted Hartree-Fock and exact diagonalizations, we unravel a very rich phase diagram controlled by the strength of both local and off-site Coulomb interactions and by the interorbital hopping anisotropy ratio t'/t. Three robust unconventional electronic phases, a pinball liquid, an inverse pinball liquid, and a large-unit-cell radical12 x radical12 droplet phase, are found to be generic in the triangular geometry, being controlled by the band structure parameters. The latter are also stabilized in the isotropic limit of our microscopic model, which recovers the standard SU(2) spinful extended single-band Hubbard model.
We argue that the hump observed in the optical conductivity at or below a few hundreds of cm(-1), in overdoped cuprates such as the electron-doped Nd(2-x)Ce(x)CuO(4-y) at x > or approximately equal ...to 0.15 and the hole-doped Bi2Sr2CuO6 and La2-xSrxCuO4, cannot be accounted for within a single-fluid description. We propose instead an interpretation based on the direct excitation of charge collective modes, which become nearly critical in the proximity to a charge-ordering instability. Their critical character entails a peculiar temperature dependence and a pseudoscaling form of the optical spectra, which agree with the experimental data.
In this paper we investigate the optical spectra of one hole in the Holstein-t-J model. We employ a dynamical mean-field theory which becomes exact in the limit of infinite connectivity. This allow ...us to investigate the local (incoherent) features which are related to the internal structure of the polaron, disregarding coherent motion associated with the Drude-like peak. We show that magnetic and electron-phonon interactions sustain each other in establishing polaronic regime. Polaron formation is reflected in a peculiar mid-infrared (MIR) band which is however notably different in the case of a lattice or magnetic origin. The dependence of σ(ω) on the electron-phonon coupling constant λ, on the exchange interaction J and on temperature T is investigated. We compare our results with experimental data in Nd2-xCexCuO4 showing that the doping and temperature dependences of the optical conductivity in this compounds is naturally reproduced by a spin/lattice polaronic model.
In a Kenyan mangrove, we studied the interactions between the gastropod Terebralia palustris and the crab Neosarmatium smithi when foraging on decaying mangrove leaves. Interactions are considerable ...on account of their wide overlap in zonation (Rhizophora mucronata belt), food items (mangrove leaves) and activity window (diurnal low water).
The last 20 years witnessed a real paradigm shift concerning the impact of biotic factors on ecosystem functions as well as on vegetation structure of mangrove forests. Before this small scientific ...revolution took place, structural aspects of mangrove forests were viewed to be the result of abiotic processes acting from the bottom-up, while, at ecosystem level, the outwelling hypothesis stated that mangroves primary production was removed via tidal action and carried to adjacent nearshore ecosystems where it fuelled detrital based food-webs. The sesarmid crabs were the first macrofaunal taxon to be considered a main actor in mangrove structuring processes, thanks to a number of studies carried out in the Indo-Pacific forests in the late 1970s and early 1980s. Following these classical papers, a number of studies on Sesarmidae feeding and burrowing ecology were carried out, which leave no doubts about the great importance of these herbivorous crabs in structuring and functioning Old world ecosystems. Although Sesarmidae are still considered very important in shaping mangrove structure and functioning, recent literature emphasizes the significance of other invertebrates. The Ocypodidae have now been shown to have the same role as Sesarmidae in terms of retention of forest products and organic matter processing in New world mangroves. In both New and Old world mangroves, crabs process large amounts of algal primary production, contribute consistently to retention of mangrove production and as ecosystem engineers, change particle size distribution and enhance soil aeration. Our understanding of the strong impact of gastropods, by means of high intake rates of mangrove products and differential consumption of propagules, has changed only recently. The role of insects must also be stressed. It is now clear that older techniques used to assess herbivory rates by insects strongly underestimate their impact, both in case of leaf eating and wood boring species and that herbivorous insects can potentially play a strong role in many aspects of mangrove ecology. Moreover, researchers only recently realized that ant–plant interactions may form an important contribution to our understanding of insect–plant dynamics in these habitats. Ants seem to be able to relieve mangroves from important herbivores such as many insects and sesarmid crabs. It thus seems likely that ants have positive effects on mangrove performance.
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