We calculate the photoemission spectral function of the one-dimensional Hubbard model away from half filling using the dynamical density matrix renormalization group method. An approach for calculating momentum-dependent quantities in finite open chains is presented. Comparison with exact Bethe Ansatz results demonstrates the unprecedented accuracy of our method. Our results show that the photoemission spectrum of the quasi-one-dimensional conductor TTF-TCNQ provides evidence for spin-charge separation on the scale of the conduction band width.PACS numbers: 71.10. Fd, 71.10.Pm, 79.60.Fr, 71.20.Rv The Luttinger liquid theory describes the ground state and asymptotic low energy properties of one-dimensional correlated metals [1]. Two characteristics of a Luttinger liquid are the absence of quasi-particles predicted by the Fermi liquid theory of normal metals and the occurrence of independent spin and charge excitations. In principle, these features can be observed in the spectral function [2,3] which corresponds to the spectrum measured in angle-resolved photoemission spectroscopy (ARPES) experiments. In real materials, however, the low-energy properties are likely to be governed by threedimensional physics. One-dimensional physics is observed only above a crossover energy scale, even in the most strongly anisotropic materials. Consequently, it has proven difficult to observe unambiguous evidence for Luttinger liquid physics in experiments probing only lowenergy properties of quasi-one-dimensional conductors.A recent ARPES experiment for the quasi-one-dimensional organic conductor TTF-TCNQ (tetrathiafulvalene tetracyanoquinodimethane) has revealed significant discrepancies from the predictions of Fermi liquid theory and conventional electronic structure calculations [4,5]. The experimental spectrum dispersion can be consistently mapped over the scale of the conduction band width onto separated spin and charge excitation bands of the one-dimensional Hubbard model [6] away from half filling. This is one of the strongest pieces of experimental evidence for spin-charge separation and thus for Luttinger liquid physics in low-dimensional materials. However, a direct comparison of the experimental ARPES spectrum with the Hubbard model spectral function has not been possible yet.The Hubbard model was solved exactly 36 years ago [7] and the dispersion of its excitation bands can be computed [8]. Nevertheless, the photoemission spectral function can only be calculated exactly in the limiting cases of noninteracting electrons or infinitely strong electron interaction [9,10] and in the low-energy limit described by the Luttinger liquid theory. Various numerical methods have provided a qualitative picture of spectral functions in the Hubbard model but exact diagonalizations [10,11] are limited to too small systems to investigate the thermodynamic limit while other approaches [12,13] are based on various approximations of uncertain accuracy.We have determined the photoemission spectral function of the one-dimensional Hubbard...
We have studied the electronic structure of the spin-1/2 quantum magnet TiOCl by polarizationdependent momentum-resolved photoelectron spectroscopy. From that, we confirm the quasi-onedimensional nature of the electronic structure along the crystallographic b-axis and find no evidence for sizable phonon-induced orbital fluctuations as origin for the non-canonical phenomenology of the spin-Peierls transition in this compound. A comparison of the experimental data to our own LDA+U and Hubbard model calculations reveals a striking lack of understanding regarding the quasi-one-dimensional electron dispersions in the normal state of this compound.
We investigate the dynamical spin and charge structure factors and the one-particle spectral function of the one-dimensional extended Hubbard model at half band-filling using the dynamical density-matrix renormalization group method. The influence of the model parameters on these frequency- and momentum-resolved dynamical correlation functions is discussed in detail for the Mott-insulating regime. We find quantitative agreement between our numerical results and experiments for the optical conductivity, resonant inelastic X-ray scattering, neutron scattering, and angle-resolved photoemission spectroscopy in the quasi-one-dimensional Mott insulator SrCuO$_2$.Comment: 9 pages, 11 figure
We report a resonant inelastic x-ray scattering study of charge excitations in the quasi-onedimensional Mott insulator SrCuO2. We observe a continuum of low-energy excitations, the onset of which exhibits a small dispersion of ∼ 0.4 eV. Within this continuum, a highly dispersive feature with a large sinusoidal dispersion (∼ 1.1 eV) is observed. We have also measured the optical conductivity, and studied the dynamic response of the extended Hubbard model with realistic parameters, using a dynamical density-matrix renormalization group method. In contrast to earlier work, we do not find a long-lived exciton, but rather these results suggest that the excitation spectrum comprises a holon-antiholon continuum together with a broad resonance.PACS numbers: 78.70. Ck, 71.10.Fd, 75.10.Pq The separation of spin and charge degrees of freedom is one of the most important and fascinating properties of electrons in strongly correlated systems in one dimension. In particular, it is well known that in the one-dimensional (1D) Hubbard model, the low-energy physics is dominated by collective excitations of decoupled charge and spin degrees of freedom called holons and spinons, respectively [1]. Experimentally, if one creates a hole by removing an electron, this hole is expected to decay into a spinon and a holon, which can be studied with angle resolved photoemission spectroscopy (ARPES) [2]. The situation is different for so-called "particle-hole" probes, such as optical spectroscopy, resonant inelastic x-ray scattering (RIXS), and electron energy loss spectroscopy (EELS). In these experiments, the total charge is conserved in the scattering process, so that an electron is simply moved from one site to another, creating a hole and a doubly occupied site. The decay of the hole creates a holon and a spinon, while the double-occupancy decays into an antiholon and a spinon. Since photons and electrons strongly couple to the charge sector, the behavior of holon-antiholon pairs can be studied with these particle-hole probes [3,4].The so-called corner-sharing chain cuprates Sr 2 CuO 3 and SrCuO 2 are both charge-transfer insulators; that is, they have insulating gaps of ∼ 2 eV arising from strong electron correlations. Since their crystal structure is highly anisotropic, the electronic structure remains 1D over a wide temperature range. Only at a very low temperature does magnetic order set in, due to the small interchain coupling (T N ≈ 2 K for SrCuO 2 [5]). Based on the commonly-used measure of quasi-one-dimensionality, T N /J ∼ 10 −3 , these compounds can be regarded as among the best realizations of quasi-1D systems [6] In this Letter, we report a detailed study of the momentum dependence of the low-energy charge excitations in SrCuO 2 , utilizing the RIXS technique. We observe a continuum of excitations arising from the creation of particle and hole pairs. Within this continuum, a welldefined spectral feature with a large sinusoidal dispersion (∼ 1.1 eV) is observed. We have also measured the optical conductivity σ(ω) and carri...
We consider the one-dimensional extended Hubbard model in the presence of an explicit dimerization δ. For a sufficiently strong nearest neighbour repulsion we establish the existence of a quantum phase transition between a mixed bond-order wave and charge-density wave phase from a pure bond-order wave phase. This phase transition is in the universality class of the two-dimensional Ising model.
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