742 research outputs found
On Hadamard Type Inequalities Involving Several Kind of Convexity
In this paper, we not only give the extensions of the results given in [7] by
Gill et al. for log-convex functions, but also obtain some new Hadamard type
inequalities for log-convex, m-convex and (alpha,m)-convex functions.Comment: This paper is published in Journal of Inequalities and Application
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Taha Toros Arşivi, Dosya No: 36-Ziya Gökalpİstanbul Kalkınma Ajansı (TR10/14/YEN/0033) İstanbul Development Agency (TR10/14/YEN/0033)Ziya Gökalp ve milli sosyoloji davamızII Ziya Gökalp ve Mehmet İzzet (1)III. Ziya Gökalp hakkında bibliyoğrafyalar ve eserlere geçmemiş bazı zikzaklı düşünceler ve inişli çıkışlı telekkiler
Breakdown of the lattice polaron picture in La0.7Ca0.3MnO3 single crystals
When heated through the magnetic transition at Tc, La0.7Ca0.3MnO3 changes
from a band metal to a polaronic insulator. The Hall constant R_H, through its
activated behavior and sign anomaly, provides key evidence for polaronic
behavior. We use R_H and the Hall mobility to demonstrate the breakdown of the
polaron phase. Above 1.4Tc, the polaron picture holds in detail, while below,
the activation energies of both R_H and the mobility deviate strongly from
their polaronic values. These changes reflect the presence of metallic,
ferromagnetic fluctuations, in the volume of which the Hall effect develops
additional contributions tied to quantal phases.Comment: 11 pages, 3 figures, final version to appear in Phys. Rev. B Rapi
Quantum coherence and carriers mobility in organic semiconductors
We present a model of charge transport in organic molecular semiconductors
based on the effects of lattice fluctuations on the quantum coherence of the
electronic state of the charge carrier. Thermal intermolecular phonons and
librations tend to localize pure coherent states and to assist the motion of
less coherent ones. Decoherence is thus the primary mechanism by which
conduction occurs. It is driven by the coupling of the carrier to the molecular
lattice through polarization and transfer integral fluctuations as described by
the hamiltonian of Gosar and Choi. Localization effects in the quantum coherent
regime are modeled via the Anderson hamiltonian with correlated diagonal and
non-diagonal disorder leading to the determination of the carrier localization
length. This length defines the coherent extension of the ground state and
determines, in turn, the diffusion range in the incoherent regime and thus the
mobility. The transfer integral disorder of Troisi and Orlandi can also be
incorporated. This model, based on the idea of decoherence, allowed us to
predict the value and temperature dependence of the carrier mobility in
prototypical organic semiconductors that are in qualitative accord with
experiments
Energy thresholds for discrete breathers in one-, two- and three-dimensional lattices
Discrete breathers are time-periodic, spatially localized solutions of
equations of motion for classical degrees of freedom interacting on a lattice.
They come in one-parameter families. We report on studies of energy properties
of breather families in one-, two- and three-dimensional lattices. We show that
breather energies have a positive lower bound if the lattice dimension of a
given nonlinear lattice is greater than or equal to a certain critical value.
These findings could be important for the experimental detection of discrete
breathers.Comment: 10 pages, LaTeX, 4 figures (ps), Physical Review Letters, in prin
Inelastic Quantum Transport
We solve a Schrodinger equation for inelastic quantum transport that retains
full quantum coherence, in contrast to previous rate or Boltzmann equation
approaches. The model Hamiltonian is the zero temperature 1d Holstein model for
an electron coupled to optical phonons (polaron), in a strong electric field.
The Hilbert space grows exponentially with electron position, forming a
non-standard Bethe lattice. We calculate nonperturbatively the transport
current, electron-phonon correlations, and quantum diffusion. This system is a
toy model for the constantly branching ``wavefunction of the universe''.Comment: revtex, 13 pages, 4 figure
Signatures of polaronic excitations in quasi-one-dimensional LaTiO
The optical properties of quasi-one-dimensional metallic LaTiO are
studied for the polarization along the and axes. With decreasing
temperature modes appear along both directions suggestive for a phase
transition. The broadness of these modes along the conducting axis might be due
to the coupling of the phonons to low-energy electronic excitations across an
energy gap. We observe a pronounced midinfrared band with a temperature
dependence consistent with (interacting) polaron models. The polaronic picture
is corroborated by the presence of strong electron-phonon coupling and the
temperature dependence of the dc conductivity.Comment: 5 pages, 5 figure
Infrared response of ordered polarons in layered perovskites
We report on the infrared absorption spectra of three oxides where charged
superlattices have been recently observed in diffraction experiments. In
LaSrNiO, polaron localization is found to suppress the
low-energy conductivity through the opening of a gap and to split the
- vibrational manifold of the oxygen octahedra. Similar effects
are detected in SrLaMnO and in LaNiO, with
peculiar differences related to the type of charge ordering.Comment: File latex, 11 p. + 3 Figures, to appear on Phys. Rev. B (Rapid
Commun.), 1 Oct. 1996. The figures will be faxed upon request.
E-mail:[email protected] Fax: +39-6-446315
Structural Disorder Induced Polaron Formation and Magnetic Scattering in the Disordered Holstein-Double Exchange Model
In this paper we present results on the disordered Holstein-Double Exchange
model, explicitly in three dimension and `metallic' densities, obtained by
using a recently developed Monte Carlo approach. Following up on our earlier
paper, cond-mat/0406085, here we provide a detailed microscopic picture of the
thermally driven metal-insulator transition (MIT) that arises close to the
ferromagnet to paramagnet transition in this problem. This paper is focused
mainly on the `diagnostics', clarifying the origin of the effective disorder
that drives the MIT in this system. To that effect, we provide results on the
thermal evolution of the distributions of (i) lattice distortions, (ii) the net
`structural disorder' and (iii) the `hopping disorder' arising from spin
randomness feeding back through the Hunds coupling. We suggest a phenomenology
for the thermally driven MIT, viewing it as an `Anderson-Holstein' transition.Comment: 6 pages, latex, JPSJ style, 7 eps figs. Style files included.
Proceedings of the SPQS Meeting at Sendai, Japan, 2004. To appear in JPS
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