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arXiv:0810.1410 · Physical Review B

Role of dynamical non-double-occupancy excitations on the quasiparticle damping of the t−J model in the large- N limit

A. Foussats, A. Greco, Matías Bejas

Published Oct 27, 2008• 5 citations
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Abstract

One-electron self-energy in the $t\ensuremath{-}J$ model was computed using a recently developed large-$N$ method based on the path-integral representation for Hubbard operators. One of the main features of the self-energy is its strong asymmetry with respect to the Fermi level, showing the spectra mostly concentrated at high negative energy. This asymmetry is responsible for the existence of incoherent structures at high negative energy in the spectral functions. It is shown that dynamical non-double-occupancy excitations are relevant for the behavior of the self-energy. It is difficult to understand the asymmetry shown by the self-energy from weak-coupling treatments. We compare our results with others in recent literature. Finally, the possible relevance of our results for the recent high energy features observed in photoemission experiments is discussed.

DOI
10.1103/physrevb.78.153110

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t−Jt-Jt−J model one-electron renormalizations: high energy features in photoemission experiments of high-TcT_cTc​ cuprates
Recent angle-resolved photoemission experiments in hole doped cuprates reported new and interesting high energy features which may be useful for understanding the electronic properties of these materials. Using a perturbative approach, which allows the calculation of dynamical properties in the t−Jt-Jt−J model, one-electron spectral properties were calculated. A strongly renormalized quasiparticle band near the Fermi surface and incoherent spectra at high energy were obtained. Among different current experimental interpretations, the obtained results are closer to the interpretation given by Pan {\it et al.}\cite{pan}. The self-energy shows large high energy contributions which are responsible for the incoherent structures showed by the spectral functions and the reduction of the quasiparticle weight and bandwidth. According to the calculation, collective charge fluctuations are the main source for the self-energy renormalizations. For testing if the obtained self-energy is compatible with transport measurement the resistivity versus temperature was estimated.
The single-particle spectral functions A(k,\ensuremath{\omega}) and self-energies \ensuremath{\Sigma}(k,\ensuremath{\omega}) are calculated within the t-J model using the finite-temperature Lanczos method for small systems. A remarkable asymmetry between the electron and hole part is found. The hole (photoemission) spectra are overdamped, with Im\ensuremath{\Sigma}\ensuremath{\propto}\ensuremath{\omega} in a wide energy range, consistent with the marginal Fermi liquid scenario, and in good agreement with experiments on cuprates. In contrast, the quasiparticles in the electron part of the spectrum show weak damping.
Employing a large-NNN scheme of the layered $t\ensuremath{-}J$ model with the long-range Coulomb interaction, which captures the fine details of the charge excitation spectra recently observed in cuprate superconductors, we explore the role of charge fluctuations on the electron self-energy. We fix the temperature at zero and focus on quantum charge fluctuations. We find a pronounced asymmetry of the imaginary part of the self-energy $\mathrm{Im}\mathrm{\ensuremath{\Sigma}}(\mathbf{k},\ensuremath{\omega})$ with respect to $\ensuremath{\omega}=0$, which is driven by strong electron correlation effects. The quasiparticle weight is reduced dramatically, which occurs almost isotropically along the Fermi surface. Concomitantly, an incoherent band and a sharp side band are generated and acquire sizable spectral weight. All these features are driven by the usual on-site charge fluctuations, which are realized in a rather high-energy region and yield plasmon excitations. On the other hand, the low-energy region with the scale of the superexchange interaction JJJ is dominated by bond-charge fluctuations. Surprisingly, compared with the effect of on-site charge fluctuations, their effect on the electron self-energy is much weaker, even if the system approaches close to bond-charge instabilities. Furthermore, quantum charge dynamics does not produce a clear kink nor a pseudogap in the electron dispersion.
Single-particle excitation spectra of the two-dimensional Hubbard model on the square lattice near half filling and at zero temperature are investigated on the basis of the self-consistent projection operator method. The method guarantees a high accuracy of the spectra with high energy and high momentum resolutions. It takes into account long-range intersite correlations as well as the strong on-site correlations. Effects of nonlocal excitations are clarified by comparing the results with those of the single-site approximation. The calculated spectra verify the quantum Monte-Carlo results for finite temperatures. The spectra at the Fermi level yield a hole-like Fermi surface in the underdoped region and an electron-like Fermi surface in the overdoped region. From a numerical analysis of the momentum dependent effective mass and self-energy, it is concluded that a marginal Fermi-liquid like state persists even at finite doping concentrations in the strongly correlated region because a van Hove singularity is pinned to the Fermi surface. It is also found that a kink structure appears in the quasiparticle energy band in the same region. The kink is shown to be caused by a mixing between the quasiparticle band and an excitation band with strong short-range antiferromagnetic correlations. These results suggest an explanation for some of the unusual properties of the normal state in high-TcT_{\rm c}Tc​ cuprates.
The flux phase predicted by the $t\text{\ensuremath{-}}J$ model in the large-NNN limit exhibits features that make it a candidate for describing the pseudogap regime of cuprates. However, certain properties, such as, for instance, the prediction of well-defined quasiparticle peaks, speak against this scenario. We have addressed these issues by computing self-energy renormalizations in the vicinity of flux phase. The calculated spectral functions show features similar to those observed in experiments. At low doping, near the flux phase, the spectral functions are anisotropic on the Fermi surface and very incoherent near the hot spots. The temperature and doping evolution of self-energy and spectral functions are discussed and compared with the experiment.