arXiv subjects

J. M. P. Carmelo

Publications and source records attributed to J. M. P. Carmelo.

At least 55 records · Page 3Linked to original sources

arXiv2006

Finite-Energy Spectral-Weight Distributions of a 1D Correlated Metal

We derive general closed-form analytical expressions for the finite-energy one- and two-electron spectral-weight distributions of an one-dimensional correlated metal with on-site electronic repulsion. Our results also provide general expressions for the one- and two-atom spectral functions of a correlated quantum system of cold fermionic atoms in a one-dimensional optical lattice with on-site atomic repulsion. In the limit of zero spin density our spectral-function expressions provide the correct zero-spin density results. Our results reveal the dominant non-perturbative microscopic many-particle mechanisms behind the exotic spectral properties observed in quasi-one-dimensional metals and correlated systems of cold fermionic atoms in one-dimensional optical lattices.

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arXiv2006

Pseudofermion scattering theory

In this paper we study the scattering theory associated with the pseudofermion dynamical theory for the Hubbard chain. In terms of pseudofermions the spectral properties are controlled by zero-momentum forward scattering only. The pseudofermion $S$ matrix is expressed as a commutative product of $S$ matrices, each corresponding to an elementary two-pseudofermion scattering event. This commutative factorization is stronger than the usual factorization associated with Yang-Baxter Equation for the original spin 1/2 electron bare $S$ matrix. Our results reveal the scattering mechanisms which control the exotic finite-energy spectral properties of the low-dimensional complex materials and correlated systems of cold fermionic atoms on an optical lattice. Importantly, the exotic scatterers and scattering centers predicted by the theory were observed by angle-resolved photoelectron spectroscopy in low-dimensional organic metals.

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arXiv2006

Scattering theories for the 1D Hubbard model

In one-dimensional (1D) non-perturbative many-electron problems such as the 1D Hubbard model the electronic charge and spin degrees of freedom separate into exotic quantum objects. However, there are two different representations for such objects and associated scattering quantities whose relation is not well understood. Here we solve the problem by finding important information about the relation between the corresponding alternative choices for one-particle scattering states. Our study reveals why one of these representations, the {\it pseudofermion} representation, is the most suitable for the description of the unusual finite-energy spectral and dynamical properties of the model. This is a problem of physical importance, since the exotic independent charge and spin finite-energy spectral features observed by angle-resolved photoelectron spectroscopy in quasi-1D metals was found recently to correspond to the charge and spin quantum objects of the pseudofermion representation.

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arXiv2006

The Hubbard model description of the photoemission TCNQ singular features

In this paper we use the pseudofermion dynamical theory (PDT) in the study of the one-electron removal singular spectral features the one-dimensional Hubbard model. The PDT reveals that in the whole $(k, ω)$-plane such features are of power-law type and correspond to well defined lines of three types: the charge singular branch lines, the spin singular branch lines, and the border lines. One of our goals is the study of the momentum and energy dependence of the spectral-weight distribution in the vicinity of such lines. We find that the charge and spin branch lines correspond to the main tetracyanoquinodimethane (TCNQ) peak dispersions observed by angle-resolved photoelectron spectroscopy in the quasi-1D organic conductor tetrathiafulvalene-tetracyanoquinodimethane (TTF-TCNQ). Our expressions refer to all values of the electronic density and on-site repulsion $U$. The weight distribution in the vicinity of the singular spectral lines is fully controlled by the overall pseudofermion phase shifts. Moreover, the shape of these lines is determined by the bare-momentum dependence of the pseudofermion energy dispersions.

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arXiv2005

General spectral function expressions of a 1D correlated model

We introduce a method that allows the evaluation of general expressions for the spectral functions of the one-dimensional Hubbard model for all values of the on-site electronic repulsion U. The spectral weights are expressed in terms of pseudofermion operators such that the spectral functions can be written as a convolution of pseudofermion dynamical correlation functions. Our results are valid for all finite energy and momentum values and are used elsewhere in the study of the unusual finite-energy properties of quasi-one-dimensional compounds and the new quantum systems of ultra-cold fermionic atoms on an optical lattice.

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arXiv2005

Correlation-function asymptotic expansions: pre-factors universality

We show that the pre-factors of all terms of the one-dimensional Hubbard model correlation-function asymptotic expansions have an universal form, as the corresponding critical exponents. In addition to calculating such pre-factors, our study clarifies the relation of the low-energy Tomonaga-Luttinger liquid behavior to the scattering mechanisms which control the spectral properties of the model at all energy scales. Our results are of general nature for many integrable interacting models and provide a broader understanding of the unusual properties of quasi-1D nanostructures, organic conductors, and optical lattices of fermionic atoms.

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arXiv2005

Spectral microscopic mechanisms and quantum phase transitions in a 1D correlated problem

In this paper we study the dominant microscopic processes that generate nearly the whole one-electron removal and addition spectral weight of the one-dimensional Hubbard model for all values of the on-site repulsion $U$. We find that for the doped Mott-Hubbard insulator there is a competition between the microscopic processes that generate the one-electron upper-Hubbard band spectral-weight distributions of the Mott-Hubbard insulating phase and finite-doping-concentration metallic phase, respectively. The spectral-weight distributions generated by the non-perturbative processes studied here are shown elsewhere to agree quantitatively for the whole momentum and energy bandwidth with the peak dispersions observed by angle-resolved photoelectron spectroscopy in quasi-one-dimensional compounds.

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arXiv2005

Scattering mechanisms and spectral properties of the one-dimensional Hubbard model

It is found that the finite-energy spectral properties of the one-dimensional Hubbard model are controlled by the scattering of charged $η$-spin-zero $2ν$-holon composite objects, spin-zero $2ν$-spinon composite objects, and charged $η$-spin-less and spin-less objects, rather than by the scattering of independent $η$-spin 1/2 holons and spin 1/2 spinons. Here $ν=1,2,...$. The corresponding $S$ matrix is calculated and its relation to the spectral properties is clarified.

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arXiv2005

Complex Electronic Behavior in a 1D Correlated Quantum Liquid

The relation of the rotated-electron site distribution configurations that describe the energy eigenstates of the one-dimensional Hubbard model to the momentum occupancy configurations of the same states associated with the Bethe ansatz quantum numbers is clarified. Our study involves the introduction of the concepts of a local pseudoparticle and an effective pseudoparticle lattice, needed for the relation of both the local pseudoparticle internal structure and the pseudoparticle occupancy configurations to the rotated-electron site distribution configurations. Our results provide further useful information about the microscopic mechanisms behind the anomalous finite-energy spectral properties of low-dimensional complex materials.

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arXiv2005

Wave-Function Factorization of the Normal-Ordered 1D Hubbard Model for Finite Values of the On-site Repulsion U

In this paper we find that in the thermodynamic limit and for the the ground-state normal-ordered 1D Hubbard model the wave function of the excited energy eigenstates which span the Hilbert subspace where the finite-number-electron excitations are contained factorizes for all values of the on-site Coulombian repulsion U. This factorization results from the absence of residual energy interactions for the pseudofermions whose occupancy configurations describe these states. Our study includes the introduction of the pseudoparticle - pseudofermion unitary transformation and of an operator algebra for both the pseudoparticles and the pseudofermions. As the corresponding pseudoparticles, the $cν$ pseudofermions (and $sν$ pseudofermions) are $η$-spin zero $2ν$-holon composite quantum objects (and spin zero $2ν$-spinon composite quantum objects) where $ν=1, 2,...$. The pseudofermion description is the most suitable for the study of the finite-energy spectral properties.

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arXiv2004

Superconductivity Driven by Chain Coupling and Electronic Correlations

We present an analysis of a system of weakly coupled Hubbard chains based on combining an exact study of spectral functions of the uncoupled chain system with a renormalization group method for the coupled chains. For low values of the onsite repulsion $U$ and of the doping $δ$, the leading instability is towards a superconducting state. The process includes excited states above a small correlation pseudogap. Similar features appear in extended Hubbard models in the vicinity of commensurate fillings. Our theoretical predictions are consistent with the phase diagram observed in the (TMTTF)$_2$X and (TMTSF)$_2$X series of organic compounds.

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arXiv2004

One-Electron Singular Branch Lines of the Hubbard Chain

The momentum and energy dependence of the weight distribution in the vicinity of the one-electron spectral-function singular branch lines of the 1D Hubbard model is studied for all values of the electronic density and on-site repulsion $U$. To achieve this goal we use the recently introduced pseudofermion dynamical theory. Our predictions agree quantitatively for the whole momentum and energy bandwidth with the peak dispersions observed by angle-resolved photoelectron spectroscopy in the quasi-1D organic conductor TTF-TCNQ.

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arXiv2004

Charge and Spin Quantum Fluids Generated by Many-Electron Interactions

In this paper we describe the electrons of the 1D Hubbard model by a fluid of unpaired rotated electrons and a fluid of zero-spin rotated-electron pairs. The rotated electrons are related to the original electrons by a mere unitary transformation. For all finite values of energy and for the whole parameter space of the model this two-fluid picture leads to a description of the energy eigenstates in terms of occupancy configurations of $η$-spin 1/2 holons, spin 1/2 spinons, and $c$ pseudoparticles only. The electronic degrees of freedom couple to external charge (and spin) probes through the holons and $c$ pseudoparticles (and spinons). Our results refer to very large values of the number of lattice sites $N_a$. The holon (and spinon) charge (and spin transport is made by $2ν$-holon (and $2ν$-spinon) composite pseudoparticles such that $ν=1,2,...$.

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arXiv2004

One and Two-Electron Spectral Function Line Shapes in the Vicinity of the Upper-Hubbard Bands Lower Limit

In this paper we derive general expressions for few-electron spectral functions of the one-dimensional Hubbard model for values of the excitation energy in the vicinity of the $M^{th}$ upper-Hubbard band lower limit. Here $M=1,2,...$ is the rotated-electron double occupation, which vanishes for the ground state and is a good quantum number for all values of the on-site Coulomb repulsion $U$. Our studies rely on a combination of symmetries of the model with a recent finite-energy holon and spinon description of the quantum problem. We apply our general scheme to the one-electron addition spectral function, dynamical structure factor, and spin singlet Cooper pair addition spectral function. Our results provide physically interesting information about the finite-energy spectral properties of the many-electron one-dimensional quantum liquid.

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arXiv2003

Normal-Ordered Wave-Function Factorization of the 1D Hubbard Model for Finite Values of the On-site Repulsion U

In this paper we find that in the thermodynamic limit and for the the ground-state normal-ordered 1D Hubbard model the wave function of excited states contained in few-electron excitations factorizes for all values of the on-site Coulombian repulsion. This factorization results from the non-interacting character of the pseudofermions whose occupancy configurations describe these excited states. Our study includes the introduction of the pseudoparticle - pseudofermion unitary transformation and of an operator algebra for both the pseudoparticles and the pseudofermions. The pseudofermions are non interacting and thus have no residual interactions, in contrast to the corresponding pseudoparticles, whose statistics we classify according to the generalized Pauli principle. The physics behind the invariance of the pseudoparticles under the above transformations for specific values of the bare momentum is also studied and discussed.

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arXiv2003

Finite-Energy Landau Liquid Theory for the 1D Hubbard Model: Pseudoparticle Energy Bands and Degree of Localization/Delocalization

This paper is part of a broader study whose main goal is the study of the finite-energy spectral properties of the non-perturbative one-dimensional (1D) Hubbard model and the evaluation of finite-energy correlation-function expressions. Here we study the deviations from the ground state values of double occupancy which result from creation or annihilation of holons, spinons, and pseudoparticles. The band-momentum dependence of the obtained double-occupancy spectra provides important information on the degree of localization/delocalization of the real-space lattice electron site distribution configurations associated with the pseudoparticles. We also study the band-momentum, on-site electronic repulsion, and electronic density dependence of the pseudoparticle energy bands. The shape of these bands plays an important role in the finite-energy spectral properties of the model. Such a shape defines the form of the lines in the momentum-energy/frequency plane where the peaks and edges of the one-electron and two-electron spectral weight of physical operators are located. Our findings are useful for the study of the one-electron and two-electron spectral weight distribution of physical operators.

cond-mat.str-el↗

arXiv2003

Finite-Energy Pseudoparticle Theory for the 1D Hubbard Model II: Holon and Spinon Dominant Processes for the Few-Electron Spectral Weight Properties

In the first paper of this series it was found that the $η$-spin 1/2 holons, spin 1/2 spinons, and $c$ pseudoparticles whose occupancy configurations describe the energy eigenstates of the one-dimensional Hubbard model emerge from the electron - rotated-electron unitary transformation. In this second paper we discuss and clarify how the relation of the electrons to the above objects can be used in a program for evaluation of finite-energy few-electron spectral functions. As a first step, here we characterize the dominant holon and spinon microscopic physical processes that originate more than 99% of the few-electron spectral weight. These dominant processes are related to exact selection rules for the values of the number of holons and spinons generated or annihilated by application onto a ground state of rotated-electron operators. We also generalize the concepts of a lower Hubbard band and upper Hubbard bands to all values of on-site Coulombian repulsion.

cond-mat.str-el↗

arXiv2003

Description of the Energy Eigenstates of the 1D Hubbard Model in Terms of Rotated-Electron Site Distribution Configurations

In this paper we describe the pseudoparticles, holons, and spinons whose occupancy configurations describe the energy eigenstates of the one-dimensional (1D) Hubbard model in terms of rotated electrons. Rotated electrons are related to electrons by a mere unitary transformation such that rotated electron double occupation is a good quantum number. Moreover, we introduce the concepts of local pseudoparticle and effective pseudoparticle lattice. Our findings provide useful information about the relation of the exotic pseudoparticles, holons, and spinons that diagonalize the non-perturbative many-electron problem to the original electrons. We provide an example showing how the derived local pseudoparticle representation can be used in the evaluation of finite-energy few-electron spectral function expressions.

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