PSEUDOGAP BEHAVIOR IN Bi₂Ca₂SrCu₂O₈: RESULTS OF GENERALIZED DYNAMICAL MEAN-FIELD APPROACH
Kuchinskii E.Z., Nekrasov L.A., Pchelkina Z.V., Sadovskii M.V.

Received: September 20, 2006

PACS: 71.10.Fd, 71.10.Hf, 71.27.+a, 71.30.+h, 74.72.-h

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Pseudogap phenomena are observed for the normal underdoped phase of different high-T_c cuprates. Among others, the Bi₂Sr₂CaCu₂O_8-δ (Bi2212) compound is one of the most studied experimentally. To describe the pseudogap regime in Bi2212, we use a novel generalized ab initio LDA+DMFT+Σ _k hybrid scheme. This scheme is based on the strategy of one of the most powerful computational tools for real correlated materials: the local density approximation (LDA) + dynamical mean-field theory (DMFT). Conventional LDA+DMFT equations are here supplied with an additional (momentum-dependent) self-energy Σ _k in the spirit of our recently proposed DMFT+Σ _k approach accounting for pseudogap fluctuations. In the present model, Σ _k describes nonlocal correlations induced by short-range collective Heisenberg-like antiferromagnetic spin fluctuations. The effective single-impurity problem of the DMFT is solved by the numerical renormalization group (NRG) method. Material-specific model parameters for the effective x²-y² orbital of Cu-3d shell of the Bi2212 compound, e.g., the values of intra- and interlayer hopping integrals between different Cu sites, the local Coulomb interaction U, and the pseudogap potential Δ were obtained within the LDA and LDA+DMFT schemes. Here, we report the theoretical LDA+DMFT+Σ _k quasiparticle band dispersion and damping, Fermi surface renormalization, momentum anisotropy of (quasi) static scattering, densities of states, spectral densities, and angular-resolved photoemission (ARPES) spectra accounting for pseudogap and bilayer splitting effects for normal (slightly) underdoped Bi2212 (δ=0.15). We show that LDA+DMFT+Σ _k successfully describes strong (pseudogap) scattering close to Brillouin zone boundaries. Our calculated LDA+DMFT+Σ _k Fermi surfaces and ARPES spectra in the presence of pseudogap fluctuations are almost insensitive to the bilayer splitting strength. However, our LDA-calculated value of bilayer splitting is found to be rather small to describe the experimentally observed peak-dip-hump structure. The results obtained are in good semiquantitative agreement with various recent ARPES experiments.