ORIGIN OF ``HOT SPOTS'' IN THE PSEUDOGAP REGIME OF Nd _1.85 Ce _0.15 CuO ₄: AN LDA+DMFT+Σ _k STUDY
Kokorina E.E., Kuchinskii E.Z., Nekrasov I.A., Pchelkina Z.V., Sadovskii M.V., Sekiama A., Suga S., Tsunekawa M.

Received: April 17, 2008

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

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Material-specific electronic band structure of the electron-doped high-T_c cuprate Nd_1.85 Ce_0.15 CuO₄ ( NCCO) is calculated in the pseudogap regime using the recently developed generalized LDA+DMFT+Σ _k scheme. The LDA/DFT (density-functional theory within local density approximation) provides model parameters (hopping integral values and local Coulomb interaction strength) for the one-band Hubbard model, which is solved by the DMFT (dynamical mean-field theory). To take pseudogap fluctuations into account, the LDA+DMFT is supplied with an ``external'' k-dependent self-energy Σ <sub>k</sub> that describes interaction of correlated conducting electrons with nonlocal Heisenberg-like antiferromagnetic ( AFM) spin fluctuations responsible for the pseudogap formation. Within this LDA+DMFT+Σ <sub>k</sub> approach, we demonstrate the formation of pronounced ``hot spots'' on the Fermi surface ( FS) map in NCCO, opposite to our recent calculations for Bi₂ Sr₂ CaCu₂ O_8-δ ( Bi2212), which have produced a rather extended region of the FS ``destruction''. There are several physical reasons for this fact: (i) the ``hot spots'' in NCCO are located closer to the Brillouin zone center; (ii) the correlation length ξ of AFM fluctuations is longer for NCCO; (iii) the pseudogap potential Δ is stronger than in Bi2212. Comparison of our theoretical data with recent bulk-sensitive high-energy angle-resolved photoemission ( ARPES) data for NCCO provides good semiquantitative agreement. Based on that comparison, an alternative explanation of the van Hove singularity at -0.3 eV is proposed. Optical conductivity for both Bi2212 and NCCO is also calculated within the LDA+DMFT+Σ _k scheme and is compared with experimental results, demonstrating satisfactory agreement.