1,721,037 research outputs found
Density of states for energy-dependent effective Hamiltonians
No full textWe provide two analytic expressions particularly useful for the evaluation of the density of states of multichannel interacting structures described by effective energy-dependent Hamiltonians. We show that the knowledge of the off-diagonal matrix elements of a properly defined Green's function, between the terminal sites of the system, is the main ingredient to obtain the total density of states. We have used our expressions to calculate the densities of states of ladder chains where each site of the chains may be connected to an external system. A couple of significant examples clarify the feasibility of these expressions
Tight-binding effective hamiltonians for the electronic properties of polyanilyne chains
No full textDensity of states of multichannel systems
No full textWe provide an analytic expression particularly useful for the evaluation of the density of states in systems which can be mapped into multichannel interacting structures. By means of the Green's function formalism and the real-space renormalization procedure, we arrive at a closed formula and we show how it can be easily implemented for numerical calculations. The application to the case of a couple of interacting chains is presented
Transport properties of emeraldine salts: The nature of the metallic state
No full textStarting from the tight-binding representation of the Hamiltonian of emeraldine salt, which reproduces the electronic structure of the polymer, we investigate the nature of its metallic state. We exploit the decimation- renormalization scheme to work with strictly one-dimensional systems (polymer chains and ladder polymers) then, by a proper account of disorder and interchain effects, we evaluate the transmittivity of the polymer by the T-matrix scattering approach. Our results support the polaronic model for the metallic island of emeraldine salt and show that using the same tight-binding parameters, the random dimer model is unable to take the Fermi level of the polymer into regions of highly transmitting states
Finite-temperature contact for a SU(2) Fermi gas trapped in a one-dimensional harmonic confinement
No full textWe calculate the finite-temperature Tan's contact for N SU(2) fermions, characterized by repulsive contact interaction, trapped in a 1D harmonic confinement within a local density approximation on top of a thermodynamic Bethe ansatz. The Tan's contact for such a system, as in the homogeneous case, displays a minimum at a very low temperature. By means of an exact canonical ensemble calculation for two fermions, we provide an explicit formula for the contact at very low temperatures that reveals that the minimum is due to the mixing of states with different exchange symmetries. In the unitary regime, this symmetry blending corresponds to a maximal entanglement entropy.Fil: Capuzzi, Pablo. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Física de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Física de Buenos Aires; ArgentinaFil: Vignolo, P.. Centre National de la Recherche Scientifique; Franci
Faraday waves in elongated superfluid fermionic clouds
Full text linkWe use hydrodynamic equations to study the formation of Faraday waves in a superfluid Fermi gas at zero temperature confined in a strongly elongated cigar-shaped trap. First, we treat the role of the radial density profile in the limit of an infinite cylindrical geometry and analytically evaluate the wavelength of the Faraday pattern. The effect of the axial confinement is fully taken into account in the numerical solution of hydrodynamic equations, and shows that the infinite cylinder geometry provides a very good description of the phenomena. © 2008 The American Physical Society.Fil: Capuzzi, Pablo. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Física de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Física de Buenos Aires; ArgentinaFil: Vignolo, P.. Universite Nice; Francia. Centre National de la Recherche Scientifique; Franci
Hydrodynamic excitations in a spin-polarized Fermi gas under harmonic confinement in one dimension
Full text linkWe consider a time-dependent nonlinear Schrodinger equation in one dimension (1D) with a fifth-order interaction term and external harmonic confinement, as a model for both (i) a Bose gas with hard-core contact interactions in the local-density approximation, and (ii) a spin-polarized Fermi gas in the collisional regime. We evaluate analytically in the Thomas-Fermi limit the density fluctuation profiles and the collective excitation frequencies, and compare the results for the low-lying modes with those obtained from numerical solution of the Schrodinger equation. We find that the excitation frequencies are multiples of the harmonic-trap frequency even in the strong-coupling Thomas-Fermi regime. This result shows that the hydrodynamic and the collisionless collective spectra coincide in the harmonically confined 1D Fermi gas, as they do for sound waves in its homogeneous analog. It also shows that in this case the local-density theory reproduces the exact collective spectrum of the hard-core Bose gas under harmonic confinement
Collective excitations of a one-dimensional Fermi gas under harmonic confinement
No full textWe study the spectrum of collective excitations of a spin-polarized Fermi gas confined in a one-dimensional harmonic trap at zero temperature. In the collisionless regime we evaluate exactly the dynamic structure factor, while in the collisional regime we solve analytically the linearized equations of hydrodynamics in the Thomas-Fermi approximation. We also verify the validity of the Thomas-Fermi theory by solving numerically a time-dependent nonlinear Schroedinger equation with a fifth-order interaction term. We find that in both the collisionless and the collisional regime the excitation frequencies of the Fermi gas are multiples of the trap frequency, analogously to the case of the one-dimensional homogeneous Fermi fluid where the velocities of zero and first sound coincide. Due to boson-fermion dynamical mapping our results for the spectrum apply as well to a one-dimensional Bose gas with hard-core point-like interactions ("Tonks gas")
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