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. The finite-energy spectral dispersions recently observed in quasi-one-dimensional (1D) metals by angle-resolved photoelectron spectroscopy (ARPES) reveal significant discrepancies from the conventional band-structure description [1, 2]. The study of the microscopic mechanisms behind these unusual finite-energy spectral properties remains until now an interesting open problem. There is some evidence that the correlation effects described by the 1D Hub-bard model might contain such finite-energy mechanisms [1, 2]. However, for finite values of the on-site repulsion U very little is known about its finite-energy spectral properties, in contrast to simpler models [3]. Bosonization [4] and conformal-field theory [5] do not apply at finite energy. For U → ∞ the method of Ref. [6] provides valuable qualitative information, yet a quantitative description of the finite-energy spectral properties of quasi-1D metals requires the solution of the problem for finite values of U. The method of Ref. [7] refers to features of the insulator phase. For U ≈ 4t, where t is the transfer integral, there are numerical results for the one-electron spectral function [8] which, unfortunately, provide very little information about the microscopic mechanisms behind the finite-energy spectral properties. Recent preliminary results obtained by use of the finite-energy holon and spinon description introduced in Refs. [9–11] predict separate one-electron charge and spin spectral branch lines [1]. For the electron-removal spectral function these lines show quantitative agreement with the peak dispersions observed by ARPES in the quasi-1D organic conductor TTF-TCNQ [1]. However,