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arXiv:cond-mat/9506110 · Physical review. B, Condensed matter

Charge-spin separation in 2D Fermi systems: Singular interactions as modified commutators, and solution of the 2D Hubbard model in the bosonized approximation

Philip Warren Anderson, Dmitri V. Khveshchenko

Published Dec 15, 1995• 16 citations
arXivHTMLPDF

Abstract

The general two-dimensional fermion system with repulsive interactions (typified by the Hubbard model) is bosonized, taking into account the finite on-shell forward-scattering phase shift derived in earlier papers. By taking this phase shift into account in the bosonic commutation relations, a consistent picture emerges showing the charge-spin separation and anomalous exponents of the Luttinger liquid.

DOI
10.1103/physrevb.52.16415

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The general two-dimensional fermion system with repulsive interactions (typified by the Hubbard model) is bosonized, taking into account the finite on-shell forward-scattering phase shift derived in earlier papers. By taking this phase shift into account in the bosonic commutation relations, a consistent picture emerges showing the charge-spin separation and anomalous exponents of the Luttinger liquid.
The problem of spin-charge separation is addressed by considering current carrying states in a one-dimensional system of interacting electrons. Exact results for the Hubbard model and the bosonization method are exploited. We find that away from half filling both spin and charge excitations carry charge currents which are proportional to their momenta for most cases. Being in a qualitative agreement with the noninteracting ld Fermi gas picture, this result contradicts the spin-charge separation concept as it is usually derived e.g. from the bosonization approach or in a strong repulsion picture. For weak coupling the paradox is resolved by taking into account the Fermi velocity dispersion and by reexamining the structure of the current operator within the bosonization approach. For strong coupling we recover an effect of hale drag by a spinon as reflected in their momentum shifts.
We compute the spectral function rho (q, omega ) of the one-dimensional Luttinger model. We discuss the distinct influences of charge-spin separation and of the anomalous dimensions of the fermion operators and their evolution with correlation strength. Charge-spin separation shows up in finite spectral weight at frequencies between v sigma q and v rho q, where v sigma and v rho are the velocities of spin and charge fluctuations, while spectral weight above v rho q and below -v rho q is generated by the hybridization of the Fermi surface at +or-k F by interactions. There are non-universal power-law singularities at these special frequencies. We discuss the consistency of recent photoemission experiments on low-dimensional conductors with a Luttinger-liquid picture, which then would suggest very strong long-range interactions. It is pointed out that many-particle correlation functions in principle exhibit similar singularities, but they probe different and complementary aspects of the Fermi-surface interactions.
Non-Fermi liquid behavior is found for the first time in a two-dimensional (2D) system with non-singular interactions using Haldane’s bosonization scheme. The bosonized system is solved exactly by a generalized Bogoliubov transformation. The fermion momentum distribution, calculated using a generalized Mattis-Lieb technique, exhibits a non-universal power law in the vicinity of the Fermi surface for intermediate interaction strengths. In recent years, there has been great interest in possible non-Fermi-liquid-like behavior in the ground state of two-dimensional (2D) strongly correlated fermionic systems [1]. It is well-known that in one dimension the ground state of a fermionic system with arbitrarily weak interactions is not a Fermi liquid but a state usually known as a Luttinger liquid [2]. For the 2D case, many studies have suggested that, in the limit of weak interactions, this behavior does not appear [3]. Studies of systems with a small number of particles also suggest Fermi liquid behavior in 2D [4]. Although Khveshchenko et al have found non-Fermi-liquid behavior in 2D, they worked only with a singular long-range current-current interaction [5]. The one-dimensional Luttinger liquid solution can be obtained by a bosonization
Analysis of interacting fermion systems shows that there are two fundamentally different fixed points, Fermi-liquid theory and ``Luttinger-liquid theory'' (Haldane), a state in which charge and spin acquire distinct spectra and correlations have unusual exponents. The Luttinger liquids include most interacting one-dimensional systems, and some higher- (especially two) dimensional systems in which the band spectrum is bounded above, systems with Mott-Hubbard gaps and an upper Hubbard band. We give a theory which is useful in calculating normal-state, and some superconducting, properties of high-Tc{\mathit{T}}_{\mathit{c}}Tc​ superconductors.
A model of two interacting one-dimensional fermion systems (``Luttinger liquids'') coupled by single-particle hopping is investigated. Bosonization allows a number of exact statements to be made. In particular, for forward scattering only, the model contains two massless boson sectors and an Ising-type critical sector. For general repulsive interactions, there is a spin excitation gap and either d-type pairing or orbital antiferromagnetic fluctuations dominate. It is argued that the same behavior is also found for strong interactions. A possible scenario for the crossover to a Fermi liquid in a many-chain system is discussed. \textcopyright{} 1996 The American Physical Society.
Abstract We present a simple derivation of the Luttinger liquid relation for the one-dimensional Hubbard model, considering a finite U and in the U = ∞ limit. We describe a simple solution of the Hubbard model in the infinite repulsion limit and use it to calculate the correlators of the model in this limit in a simple and physical way using the bosonization technique. We then calculate the asymptotics of the correlators of the model at arbitrary U through a single parameter, which can be calculated from the Bethe Ansatz solution. Our derivation of the critical exponents is simple and allows one to express different physical operators of the Hubbard model through the charge and spin Bose fields in a direct and physically transparent way.