No abstract

UvA-DARE is a service provided by the library of the University of Amsterdam (http://dare.uva.nl) UvA-DARE (Digital Academic Repository)X-ray absorption spectroscopy of detwinned PrxY1-xBa2Cu3O7-y single crystals: electronic structure and hole distribution Merz, M.; Nücker, N.; Pellegrin, E.; Schweiss, P.; Schuppler, S.; Kielwein, M.; Knupfer, M.; Golden, M.S.; Fink, J. General rightsIt is not permitted to download or to forward/distribute the text or part of it without the consent of the author(s) and/or copyright holder(s), other than for strictly personal, individual use, unless the work is under an open content license (like Creative Commons). Disclaimer/Complaints regulationsIf you believe that digital publication of certain material infringes any of your rights or (privacy) interests, please let the Library know, stating your reasons. In case of a legitimate complaint, the Library will make the material inaccessible and/or remove it from the website. Please Ask the Library: http://uba.uva.nl/en/contact, or a letter to: Library of the University of Amsterdam, Secretariat, Singel 425, 1012 WP Amsterdam, The Netherlands. You will be contacted as soon as possible. Substituting Y in orthorhombic ͑Y,R)Ba 2 Cu 3 O 7 by any rare-earth element R has generally little effect on the superconducting properties. For RϭPr, however, superconductivity is completely suppressed. To understand this effect we have studied the unoccupied electronic structure of Pr x Y 1Ϫx Ba 2 Cu 3 O 7Ϫy (xϭ0.0, 0.4, 0.8) using polarization-dependent O 1s near-edge x-ray absorption spectroscopy of detwinned single crystals. We identify the hole states in the CuO 2 planes and the CuO 3 chains and give estimates of the relative contributions of the O 2p x , O 2p y , and O 2p z orbitals to these states. Along with the comparison of oxygen-rich (yϷ0.1) to the oxygen-depleted materials (yϷ0.9), this allows a test of the current theoretical explanations for the Pr-induced suppression of superconductivity. While we can rule out models involving hole filling or charge transfer between the planes and the chains, our data are consistent with approaches based on Pr 4f -O 2p hybridization. ͓S0163-1829͑97͒03313-4͔

We demonstrate that it is possible to obtain spin-resolved valence band spectra with a very high degree of spin polarization from antiferromagnetic transition metal materials if the excitation light is circularly polarized and has an energy close to the cation 2p 3͞2 (L 3 ) white line. We are able to unravel the different spin states in the single-particle excitation spectrum of CuO and show that the top of the valence band is of pure singlet character, which provides strong support for the existence and stability of Zhang-Rice singlets in high-T c superconductors. [S0031-9007(97)02343-0] PACS numbers: 74.25.Jb, 75.25. + z, To determine the nature and behavior of quasiparticles in strongly correlated transition metal oxides, including high-T c superconductors, it is highly desirable to have experimental information about the energies and band widths of the different spin and multiplet states in the single-particle excitation spectrum. Identification of these states, which have their meaning within the Anderson impurity model, could facilitate the modeling of the lowenergy excitations of the lattice in terms of those of the impurity. Knowledge of the character of the first ionization states is important for a better understanding of the behavior of the charge carriers in the doped materials, which could be quite intricate, especially when bound states occur with a compensated local spin contrary to that expected from Hund's first rule. There is a tendency for such to occur in charge transfer insulators, with perhaps the high-T c cuprates as the most famous of them. In fact, the basic assumption in main stream theories concerning high-T c superconductivity, like the single band Hubbard model [1] and the t-J model [2], is that the relevant states in the CuO 2 planes are of local singlet character, based on theoretical estimates [3][4][5][6][7]. Up to now, however, no direct experimental observation of such spin compensated states have been reported, mainly because spin-resolved photoemission [8][9][10][11], which is the obvious spectroscopic tool to use, cannot be applied due to the fact that most of the oxide materials, including the high-T c cuprates, are macroscopically not magnetic, so that all the spinresolved signals from the magnetically opposite cation sites cancel each other. For the same reason, magnetic circular dichroism experiments [12 -14] at the cation 2p and O 1s photoabsorption edges of hole doped oxides [15] and cuprates [16,17] would provide no information about the magnetic coupling between the cation and oxygen holes.In this paper we report the combined use of circularly polarized light and electron spin detection in our resonant photoemission study on CuO. Of all strongly correlated transition materials, CuO has the simplest atomic multiplet structure, and may therefore serve as a first test for this new type of spin-resolved photoemission technique applied to antiferromagnets. CuO may also serve as a model compound for high-T c cuprates, since in comparing it with the insulating parent compou...

We present temperature-dependent V-2p and O-1s x-ray-absorption spectra of LiVO 2. The aim of this study is to monitor changes in electronic structure on going through the phase transition. The spectral changes turn out to be very small: the V-3d-O-2p hybridization does not change considerably, and the symmetry of the V-ion ground state ͑high-spin 3 T 1) is retained. To explain our results, together with the anomalously low magnetic susceptibility below the transition temperature, we propose a model in which a three-orbital sublattice is formed in the V ͑111͒ planes, which results in a total singlet state. ͓S0163-1829͑97͒00623-1͔