We report high-resolution high-energy photoemission spectra together with parameter-free LDA + DMFT (local density approximation + dynamical mean-field theory) results for Sr1-xCaxVO3, a prototype 3d(1) system. In contrast to earlier investigations the bulk spectra are found to be insensitive to x. The good agreement between experiment and theory confirms the bulk sensitivity of the high-energy photoemission spectra.

We propose a computational scheme for the ab initio calculation of Wannier functions (WFs) for correlated electronic materials. The full-orbital HamiltonianĤ is projected into the WF subspace defined by the physically most relevant partially filled bands. The HamiltonianĤ W F obtained in this way, with interaction parameters calculated by constrained LDA for the Wannier orbitals, is used as an ab initio setup of the correlation problem, which can then be solved by many-body techniques, e.g., dynamical mean-field theory (DMFT). In such calculations the self-energy operator Σ(ε) is defined in WF basis which then can be converted back into the full-orbital Hilbert space to compute the full-orbital interacting Green function G(r, r ′ , ε). Using G(r, r ′ , ε) one can evaluate the charge density, modified by correlations, together with a new set of WFs, thus defining a fully selfconsistent scheme. The Green function can also be used for the calculation of spectral, magnetic and electronic properties of the system. Here we report the results obtained with this method for SrVO 3 and V 2 O 3 . Comparisons are made with previous results obtained by the LDA+DMFT approach where the LDA DOS was used as input, and with new bulk-sensitive experimental spectra.

The interface between LaAlO(3) and SrTiO(3) hosts a two-dimensional electron system of itinerant carriers, although both oxides are band insulators. Interface ferromagnetism coexisting with superconductivity has been found and attributed to local moments. Experimentally, it has been established that Ti 3d electrons are confined to the interface. Using soft x-ray angle-resolved resonant photoelectron spectroscopy we have directly mapped the interface states in k space. Our data demonstrate a charge dichotomy. A mobile fraction contributes to Fermi surface sheets, whereas a localized portion at higher binding energies is tentatively attributed to electrons trapped by O vacancies in the SrTiO(3). While photovoltage effects in the polar LaAlO(3) layers cannot be excluded, the apparent absence of surface-related Fermi surface sheets could also be fully reconciled in a recently proposed electronic reconstruction picture where the built-in potential in the LaAlO(3) is compensated by surface O vacancies serving also as a charge reservoir.

Electron correlations are known to play an important role in determining the unusual physical properties of a variety of compounds. Such properties include high-temperature superconductivity, heavy fermion behaviour and metal-to-insulator transitions. High-resolution photoelectron spectroscopy (PES) provides a means of directly probing the electronic states (particularly those near the Fermi level) in these materials, but the short photoelectron mean free paths (< or = 5 A) associated with the low excitation energies conventionally used (< or = 120 eV) make this a surface-sensitive technique. Now that high-resolution PES is possible at much higher energies, with mean free paths as long as 15 A (ref. 6), it should become feasible to probe the bulk electronic states in these materials. Here we demonstrate the power of this technique by applying it to the cerium compounds CeRu2Si2 and CeRu2. Previous PES studies of these compounds revealed very similar spectra for the Ce 4f electronic states, yet it is expected that such states should be different owing to their differing degrees of hybridization with other valence bands. Our determination of the bulk Ce 4f electronic states of these compounds resolves these differences.

We have studied the electronic structure and charge ordering (Verwey) transition of magnetite (Fe3O4) by soft X-ray photoemission. Due to the enhanced probing depth and the use of different surface preparations we are able to distinguish surface and volume effects in the spectra. The pseudogap behavior of the intrinsic spectra and its temperature dependence give evidence for the existence of strongly bound small polarons consistent with both dc and optical conductivity. Together with other recent structural and theoretical results our findings support a picture in which the Verwey transition contains elements of a cooperative Jahn-Teller effect, stabilized by local Coulomb interaction.

We report on the excellent performance of a newly constructed soft x-ray helical undulator beamline BL25SU of SPring-8 for photon energies 500-1800 eV. The full beamline was designed to perform very high resolution soft x-ray spectroscopy of solids with using high brilliance, highly circularly polarized undulator radiation. The grazing incidence monochromator employs varied-line-spacing plane gratings which operate in convergent light from a spherical mirror and focuses monochromatic light onto the exit slit. A resolving power in excess of 15 000 was measured at 540 and 870 eV for a grating with a central groove density of 600 lines/mm from the photoemission spectra of Au. A resolving power of more than 20 000 is estimated near 870 eV for a grating with a central groove density of 1000 lines/mm. A photon flux of more than 1ϫ10 11 photons/s/100 mA/0.02% b.w. is supplied onto the sample between 500 and 1800 eV with very low amount of higher-order light. The low heat load from the twin-helical undulator gives high stability to all optical components, which is essential to obtain high resolution in a wide energy region. Three experimental stations are installed in tandem on this beamline for various high resolution spectroscopy measurements.

The importance of electronic correlation effects in the layered perovskite Sr2RuO4 is evidenced. To this end we use state-of-the-art LDA+DMFT (Local Density Approximation + Dynamical MeanField Theory) in the basis of Wannier functions to compute spectral functions and the quasiparticle dispersion of Sr2RuO4. The spectra are found to be in good agreement with various spectroscopic experiments. We also calculate the k-dependence of the quasiparticle bands and compare the results with new angle resolved photoemission (ARPES) data. Two typical manifestations of strong Coulomb correlations are revealed: (i) the calculated quasiparticle mass enhancement of m * /m ≈ 2.5 agrees with various experimental results, and (ii) the satellite structure at about 3 eV binding energy observed in photoemission experiments is shown to be the lower Hubbard band. For these reasons Sr2RuO4 is identified as a strongly correlated 4d electron material.

We present the first observation of a prominent quasi-particle peak in the photoemission spectrum of the metallic phase of V2O3 and report new spectral calculations that combine the local density approximation with the dynamical mean-field theory (using quantum Monte Carlo simulations) to show the development of such a distinct peak with decreasing temperature. The experimental peak width and weight are significantly larger than in the theory.PACS numbers: PACS numbers: 71.20. Be, 71.30.+h, (V 1−x Cr x ) 2 O 3 displays a complex phase diagram with paramagnetic metal (PM), paramagnetic insulator (PI) and antiferromagnetic insulator (AFI) regions. The PM to PI transition serves as the paradigm of the MottHubbard (MH) metal-insulator transition (MIT) [1]. The MH scenario for (V 1−x Cr x ) 2 O 3 was put forth originally in the context of the half-filled one-band Hubbard model in which the tendency of the on-site Coulomb repulsion 'U ' to make a correlation gap insulator competes with the tendency of site to site hopping to make a broad band metal of bandwidth 'B'. A coherent thermodynamically consistent description of the MIT became possible with the development of the dynamical mean-field theory (DMFT) [2]. DMFT describes the strongly interacting metal in terms of Fermi liquid quasi-particles, i.e. single particle excitations near the Fermi energy E F which remain well defined as in a non-interacting system but have a self energy correction that increases their effective mass and reduces their spectral weight. In application to the Hubbard model, DMFT is significant as the best description that can be made by using a local (i.e. independent of momentum k) self energy. It may be formulated as a mapping of the lattice problem onto an effective Anderson impurity model coupled self-consistently to an effective conduction band bath [3]. In the metallic phase, although the large U value acts to separate much of the band's spectral weight away from E F into the so called upper and lower Hubbard bands, there remains at E F a distinctive quasi-particle (QP) peak, not accidentally reminiscent of the Kondo/Suhl-Abrikosov resonance [4] of the Anderson impurity model. The weight of the QPpeak decreases with increasing U/B and goes to zero at a critical value of U/B, which thus marks the MIT.Such a distinctive peak could in principle be seen in photoemission spectroscopy (PES). However, in spite of continuing efforts for over twenty years, literature [5,6,7,8,9, 10] V 3d PES spectra for the PM phase of (V 1−x Cr x ) 2 O 3 have shown at most a near E F feature that is the smallest part of the spectrum. One could hypothesize that the distinctive central peak of the halffilled one-band model is obscured and washed out by the multi-band complexity of the actual electronic structure of (V 1−x Cr x ) 2 O 3 in which the two 3d-electrons of the V 3+ ion must be distributed among singly degenerate a 1g and doubly degenerate e π g orbitals derived from a small trigonal crystal field splitting of the cubic t 2g manifold of the V 3d states....