4,220 research outputs found
Transport through a vibrating quantum dot: Polaronic effects
We present a Green's function based treatment of the effects of
electron-phonon coupling on transport through a molecular quantum dot in the
quantum limit. Thereby we combine an incomplete variational Lang-Firsov
approach with a perturbative calculation of the electron-phonon self energy in
the framework of generalised Matsubara Green functions and a Landauer-type
transport description. Calculating the ground-state energy, the dot
single-particle spectral function and the linear conductance at finite carrier
density, we study the low-temperature transport properties of the vibrating
quantum dot sandwiched between metallic leads in the whole electron-phonon
coupling strength regime. We discuss corrections to the concept of an
anti-adiabatic dot polaron and show how a deformable quantum dot can act as a
molecular switch.Comment: 10 pages, 8 figures, Proceedings of "Progress in Nonequilibrium
Green's Function IV" Conference, Glasgow 200
Thermoplastic matrix composite processing model
The effects the processing parameters pressure, temperature, and time have on the quality of continuous graphite fiber reinforced thermoplastic matrix composites were quantitatively accessed by defining the extent to which intimate contact and bond formation has occurred at successive ply interfaces. Two models are presented predicting the extents to which the ply interfaces have achieved intimate contact and cohesive strength. The models are based on experimental observation of compression molded laminates and neat resin conditions, respectively. Identified as the mechanism explaining the phenomenon by which the plies bond to themselves is the theory of autohesion (or self diffusion). Theoretical predictions from the Reptation Theory between autohesive strength and contact time are used to explain the effects of the processing parameters on the observed experimental strengths. The application of a time-temperature relationship for autohesive strength predictions is evaluated. A viscoelastic compression molding model of a tow was developed to explain the phenomenon by which the prepreg ply interfaces develop intimate contact
Phonon-affected steady-state transport through molecular quantum dots
We consider transport through a vibrating molecular quantum dot contacted to
macroscopic leads acting as charge reservoirs. In the equilibrium and
nonequilibrium regime, we study the formation of a polaron-like transient state
at the quantum dot for all ratios of the dot-lead coupling to the energy of the
local phonon mode. We show that the polaronic renormalization of the dot-lead
coupling is a possible mechanism for negative differential conductance.
Moreover, the effective dot level follows one of the lead chemical potentials
to enhance resonant transport, causing novel features in the inelastic
tunneling signal. In the linear response regime, we investigate the impact of
the electron-phonon interaction on the thermoelectrical properties of the
quantum dot device.Comment: 11 pages, 7 figures, FQMT11 Proceeding
Uniform electron gases
We show that the traditional concept of the uniform electron gas (UEG) --- a
homogeneous system of finite density, consisting of an infinite number of
electrons in an infinite volume --- is inadequate to model the UEGs that arise
in finite systems. We argue that, in general, a UEG is characterized by at
least two parameters, \textit{viz.} the usual one-electron density parameter
and a new two-electron parameter . We outline a systematic
strategy to determine a new density functional across the
spectrum of possible and values.Comment: 8 pages, 2 figures, 5 table
On the Groundstate of Yang-Mills Quantum Mechanics
A systematic method to calculate the low energy spectrum of SU(2) Yang-Mills
quantum mechanics with high precision is given and applied to obtain the
energies of the groundstate and the first few excited states.Comment: 4 pages REVTEX twocolumn, no figures; important calculational mistake
corrected which considerably changes the conclusions; references adde
Division, adjoints, and dualities of bilinear maps
The distributive property can be studied through bilinear maps and various
morphisms between these maps. The adjoint-morphisms between bilinear maps
establish a complete abelian category with projectives and admits a duality.
Thus the adjoint category is not a module category but nevertheless it is
suitably familiar. The universal properties have geometric perspectives. For
example, products are orthogonal sums. The bilinear division maps are the
simple bimaps with respect to nondegenerate adjoint-morphisms. That formalizes
the understanding that the atoms of linear geometries are algebraic objects
with no zero-divisors. Adjoint-isomorphism coincides with principal isotopism;
hence, nonassociative division rings can be studied within this framework.
This also corrects an error in an earlier pre-print; see Remark 2.11
Optical conductivity of polaronic charge carriers
The optical conductivity of charge carriers coupled to quantum phonons is
studied in the framework of the one-dimensional spinless Holstein model. For
one electron, variational diagonalisation yields exact results in the
thermodynamic limit, whereas at finite carrier density analytical
approximations based on previous work on single-particle spectral functions are
obtained. Particular emphasis is put on deviations from weak-coupling,
small-polaron or one-electron theories occurring at intermediate coupling
and/or finite carrier density. The analytical results are in surprisingly good
agreement with exact data, and exhibit the characteristic polaronic excitations
observed in experiments on manganites.Comment: 23 pages, 11 figure
Effective one-band electron-phonon Hamiltonian for nickel perovskites
Inspired by recent experiments on the Sr-doped nickelates,
, we propose a minimal microscopic model capable to describe
the variety of the observed quasi-static charge/lattice modulations and the
resulting magnetic and electronic-transport anomalies. Analyzing the motion of
low-spin (s=1/2) holes in a high-spin (S=1) background as well as their their
coupling to the in-plane oxygen phonon modes, we construct a sort of
generalized Holstein t-J Hamiltonian for the planes, which contains
besides the rather complex ``composite-hole'' hopping part non-local spin-spin
and hole-phonon interaction terms.Comment: 12 pages, LaTeX, submitted to Phys. Rev.
Connecting geodesics and security of configurations in compact locally symmetric spaces
A pair of points in a riemannian manifold makes a secure configuration if the
totality of geodesics connecting them can be blocked by a finite set. The
manifold is secure if every configuration is secure. We investigate the
security of compact, locally symmetric spaces.Comment: 27 pages, 2 figure
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