Eur. Phys. J. B 37, 15–18 (2004) DOI: 10.1140/epjb/e2004-00025-1 T HE EUROPEAN P HYSICAL JOURNAL B Energy scales and quasiparticle properties in an extended Hubbard model for HTC R. Citro a and M. Marinaro Dipartimento di Fisica “E.R. Caianiello” and Unit`a INFM di Salerno Universit`a di Salerno, Via S. Allende, 84081 Baronissi (Sa), Italy Received 31 July 2003 / Received in final form 17 November 2003 Published online 19 February 2004 – c  EDP Sciences, Societ`a Italiana di Fisica, Springer-Verlag 2004 Abstract. By means of a strong-coupling approach, developed in previous works, we study the quasiparticle properties in an extended Hubbard model in presence of critical charge fluctuations near a stripe-quantum critical-point. We show that the quasiparticle dispersion has a kink along the diagonal Brillouin zone at the energy of the order 50 meV, for realistic values of the parameters. The energy and momentum distribution curves (EDC, MDC) along the diagonal are also analyzed. The results for the EDC derived quasiparticle width reveals an anomalous drop in the low-energy scattering rate at the same energy of the kink. This drop corresponds to a new energy scale in the system that reflects the interaction between the quasiparticles and the critical charge fluctuations. The results offer a possible interpretation of the ARPES and photoemission experiments on Bi2212. PACS. 71.10.Fd Lattice fermion models (Hubbard model, etc.) – 71.10.Hf Non-Fermi-liquid ground states, electron phase diagrams and phase transitions in model systems The knowledge of multiple energy scales in physical systems provides significant insight into the processes that govern their low-energy properties. Concerning high- temperature superconductors, whose unusual properties are continuously under debate, the possibility to have mul- tiple energy scales has been well investigated in the su- perconducting state of Bi2212 throughout the Brillouin zone. Remarkably, the presence of a second energy scale has been revealed in ARPES experiments on the diagonal zone where the superconducting gap vanishes [2,3], with significant changes both in the spectral lineshape and the quasiparticle dispersion. Specifically, below T c a kink in the dispersion of quasiparticle develops along the diagonal line at finite energy (≃ 50 ± 10 meV) resulting in a change of the quasiparticle velocity up to a factor of two or more. This effect is enhanced in the underdoped sample and per- sists above T c where the kink becomes rather broad. The electronic structure calculation [1] predicts a linear disper- sion in this range, but experimental doping, temperature and k-dependence of the kink dispersion put constraints on a microscopic theory. Various interpretations on the origin of the kink have been proposed. A possible inter- pretation is based on the electron-phonon interaction [4]. A second interpretation is based on the coupling of the electrons to a magnetic resonance [5–7] and the third one is simply related to the opening of the superconducting a e-mail: citro@sa.infn.it gap which is of the order of the kink energy. In this note we present a possible interpretation of the experimental data based on the stripe-scenario in which an incommen- surate charge density wave (ICDW) is proposed as the source of the quasiparticle scattering that gives origin to the kink [8]. Within this scenario, we analyze the quasi- particle properties in an extended Hubbard model in two dimensions in presence of an ICDW. We report the results of the MDC (Momentum Distribution Curves) and of the EDC (Electron Distribution Curves) and discuss the influ- ence of the stripe order on the evolution of the quasiparti- cle peak, dispersion and width. Our results give evidence of a kink in the quasiparticle dispersion along the diagonal Brillouin zone when charge stripes start to be formed. The analysis is based on our recent work where the study of a charge vertex, as a function of the doping and momen- tum, has shown a singular behavior responsible for a stripe phase formation [9]. The occurrence of such instability can be theoretically understood as an interplay between phase separation (PS) and long-range Coulomb interaction at fi- nite doping [10]. Recently, various experimental evidences for the existence of such instability in the phase diagram of high-T c cuprates have been obtained by STM [12] and other experimental techniques (see Ref. [11]). Our results are not affected by the superconducting gap that is zero along the diagonal. A direct comparison with experimen- tal results on Bi2212 is discussed.