Search

The material-specific electronic band structure of the electron-doped high- T c cuprate Nd1.85Ce0.15CuO4 (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 k 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 k approach, we demonstrate the formation of pronounced hot spots on the Fermi surface (FS) map in NCCO, opposite to our recent calculations for Bi2Sr2CaCu2O8 − 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 + Δ k scheme and is compared with experimental results, demonstrating satisfactory agreement. [ABSTRACT FROM AUTHOR]

We have performed soft x-ray angle-resolved photoemission spectroscopy (ARPES) for the electron-doped high-temperature superconducting cuprates (HTSCs) Nd2-xCexCuO4 (x = 0.075 and 0.15) in order to disclose their genuine bulk electronic structures. Our soft x-ray ARPES has revealed that the bulk-derived nodal 'kink' (the abrupt change of the electron velocity in quasiparticle dispersions), being absent in the low-energy ARPES, is clearly observable for the electron-doped superconducting Nd1.85Ce0.15CuO4. This result confirms that the antiferromagnetic spin correlation is suppressed and the electron-phonon interactions are prevailing in the bulk of the electrondoped superconducting Nd2-xCexCuO4 at the optimal doping level. The nodal 'kink' behavior is equivalent to that observed in the hole-doped HTSCs. The anisotropic strong electron-phonon interactions seem to be inherent in the HTSCs irrespective of the type of doped carriers. [ABSTRACT FROM AUTHOR]

Abstract: We report on a high-energy angle-resolved photoemission (ARPES) study of the n-type high- cuprate, Nd1.85Ce0.15CuO4 (NCCO). Our bulk sensitive results suggest a hole-like Fermi surface as seen by the so far reported low-energy ARPES studies. The soft X-ray Cu 2p core-level photoemission spectra show clear polar-angle dependence, suggesting the difference in electron states between the bulk and surface. [Copyright &y& Elsevier]

Abstract: CeRh3B2 is a ferromagnet with exceptionally high Curie temperature ( K) among the Ce compounds with no transition metal magnetic element. Magnetic circular dichroism of soft X-ray photoabsorption (XMCD) has revealed that the orbital angular momentum of Ce 4f electron is quenched to some extent. In addition, preferential occupation of the Ce 4f orbital pointing to the c-axis has been confirmed by the soft X-ray photoabsorption measurements with different geometries. On the other hand, resonant photoemission around the Ce 3d  4f photoabsorption edge has been adopted in order to disentangle the Ce 4f and Rh 4d components in the valence band. The Rh 4d spectrum is qualitatively consistent with the band structure calculation. Although the Ce 4f spectrum has a peak near the Fermi level, the spectral shape is qualitatively different from that of the typical Kondo materials and is rather similar to that of itinerant Ce 4f systems. [Copyright &y& Elsevier]

Abstract: We have investigated the bulk and surface electronic structures of Sm4As3 by using hard and soft X-ray photoemission spectroscopies (PESs). The valence band spectral shape changes much with photon energies ( s) due to the variation of both photoionization cross sections and bulk sensitivity. PES with the wide range of s between 220 and 2450 eV demonstrates that the valence of the Sm ions is definitely trivalent in the bulk and divalent at the surface. [Copyright &y& Elsevier]

Abstract: We have performed the bulk-sensitive high-resolution soft X-ray photoemission study of a Kondo semiconductor CeRhAs and related compounds CeNiSn and CePdSn. The comparison of the spectra of polycrystalline CePdSn on the fractured and scraped surfaces show that the fracturing of the samples is much better than the scraping in order to obtain intrinsic photoemission spectra. The Ce 4d core-level spectra show clear differences in the electronic states among the materials. [Copyright &y& Elsevier]

Abstract: The metal–insulator (MI) transition in quasi-one-dimensional compound V6O13 has been investigated by angle-resolved photoemission spectroscopy (ARPES) at the photon energy of  eV using synchrotron radiation and optical study below 2 eV. Along the direction, a clear Fermi cutoff and a band dispersion near are observed in the ARPES spectra. The energy distribution curves (EDC) show an opening of a gap 0.2 eV across the transition temperature  K. The ARPES at  eV is confirmed to be a bulk-sensitive spectroscopy with high resolutions in energy and momenta. [Copyright &y& Elsevier]

Abstract: We report bulk 4f and non-4f spectral functions near the Fermi level () of a Kondo semiconductor CeRhAs and its related compound CePdSn by virtue of high-resolution soft X-ray photoemission. The non-4f spectrum of CeRhAs measured at 20K shows a shoulder at the binding energy of and almost negligible spectral weight at . Although a peak similar to a tail of the Kondo resonance is observed in the 4f spectrum of CeRhAs, the intensity at is suppressed compared with those of metallic Ce compounds. These facts are attributed to signatures of the formation of a pseudo-gap in CeRhAs. [Copyright &y& Elsevier]

We have investigated the electronic structure of A-site ordered CaCu 3 Ti 4 O 12 as a function of temperature by using angle-integrated and -resolved photoemission spectroscopies. Intrinsic changes of the electronic structure have been successfully observed in the valence band region by the careful consideration of charging effects. The obtained photoemission results have revealed that the intensity of the nearly non-dispersive Cu 3 d -O 2 p hybridized bands at the binding energy of ∼2 eV increases with decreasing temperature from 300 to 120 K. This suggests that the density of the localized states, caused by the strong correlation effects, enhances as the temperature decreases. • Temperature-dependent electronic structure of A-site ordered perovskite CaCu 3 Ti 4 O 12 has been investigated by photoemission spectroscopies. • The charging effects have been carefully considered in photoemission measurements. • The intensity of the nearly non-dispersive Cu 3 d -O 2 p hybridized bands at ∼2 eV increases with decreasing temperature. • This suggests the enhancement of the density of the localized states with decreasing temperature. [ABSTRACT FROM AUTHOR]

We have performed the photoemission and inverse photoemission experiments to elucidate the origin of Mott insulating states in A-site ordered perovskite CaCu 3 Ti 4 O 12 (CCTO). Experimental results have revealed that Cu 3 d –O 2 p hybridized bands, which are located around the Fermi level in the prediction of the local-density approximation (LDA) band calculations, are actually separated into the upper Hubbard band at ~1.5 eV and the lower Hubbard band at ~−1.7 eV with a band gap of ~1.5–1.8 eV. We also observed that Cu 3 d peak at ~−3.8 eV and Ti 3 d peak at ~3.8 eV are further away from each other than as indicated in the LDA calculations. In addition, it is found that the multiplet structure around −9 eV includes a considerable number of O 2 p states. These observations indicate that the Cu 3 d and Ti 3 d electrons hybridized with the O 2 p states are strongly correlated, which originates in the Mott-insulating states of CCTO. [ABSTRACT FROM AUTHOR]

Abstract: The electronic states of in the two-dimensional metal phase have been revealed by the high-resolution Mn resonant photoemission. The vanishingly weak intensity at indicates an anomalous metal due to the two-dimensionality of the electronic states. [Copyright &y& Elsevier]

Abstract: We have performed the bulk sensitive Mn 2p–3d resonant photoemission for Nd1−xSrxMnO3 (, 0.47, 0.50, 0.63) in order to reveal the Mn 3d electronic states. We will report the temperature and doping dependence of the Mn 3d spectral functions. The sudden spectral change for across the FM-COI transition shows the strong influence of the charge-ordering on the Mn 3d electronic states. [Copyright &y& Elsevier]

Abstract: Bulk electronic structures of Pr-based filled skutterudites and their reference materials have been investigated by bulk-sensitive photoemission spectroscopy using soft and hard X-rays. For Pr – resonance, a strong intensity in the vicinity of Fermi level () is observed only for PrFe4P12. Furthermore, PrFe4P12 has the significant spectral weight of the final state in Pr core-level spectrum. We interpret that the observed prominent intensity just below arises from a Kondo resonance due to the strong hybridization between the Pr and conduction states. [Copyright &y& Elsevier]