Momentum distribution and non-Fermi liquid behaviour in low-doped   two-orbital model: finite-size cluster quantum Monte Carlo approach
  The two-dimensional two-orbital Hubbard model is studied with the use of finite-size cluster worldline quantum Monte Carlo algorithm. This model is widely used for simulation of the band structure of FeAs clusters, which are structure elements of Fe-based high-temperature superconductors. The choice of a special basis set of hyper-sites allowed to take into account four-fermion operator terms and to overcome partly the sign problem. Spectral functions and the density of states for various parameters of the model are obtained in the undoped and low-doped regimes. The correlated distortion of the spectral density with the change of doping is observed, and the applicability of the "hard-band" approximation in the doped regime is demonstrated. Profiles of the momentum distribution are obtained for the first Brillouin zone; they have pronounced jump near the Fermi level, which decreases with the growth of the strength of the interaction. The invariance of the Fermi surface with respect to the strength of the interaction is testified. Nesting is found in the case of electron and hole doping. Fermi-liquid parameters of the model are derived. Z-factor grows sharply with the increasing the level of doping, and monotonously decreases with the growth of the strength of the interaction. Moreover, electron-hole doping asymmetry of the Z-factor is revealed. The non-Fermi liquid behaviour and the deviation from Luttinger theorem are observed. 
Vladimir A. Kashurnikov, Andrey V. Krasavin, and Yaroslav V.   Zhumagulov
cond-mat.str-el