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We report a combined valence band photoemission and Auger spectroscopy study of single crystalline Ca(Fe,Co)2As2 and Ba(Fe,TM)2As2 with transition metal TM = Ni or Cu. The valence band photoemission data show directly that the TM states move to higher binding energies with increasing atomic number,contnbuting less and less to the states close to the Fermi level. Furthermore, the 3d8 final state of the LV V Auger decay, which is observed for Ni and Cu, unambiguously reveals the accumulation of charge at these impurities. We also show that the onsite Coulomb interaction on the impurity strongly increases when moving from Co over Ni to Cu. Our results quantify the impurity potentials and imply that the superconducting state is rather robust against impurity scattering. [ABSTRACT FROM AUTHOR]

We assess the capabilities of magnetic resonant inelastic x-ray scattering (RIXS) at the O K edge in undoped cuprates by taking La2CuO4 as a benchmark case, based on a series of RIXS measurements that we present here. By combining the experimental results with basic theory we point out the fingerprints of bimagnon excitation in the O K edge RIXS spectra. These are a dominant peak around 450 meV, the almost complete absence of dispersion both with π and &sgr; polarization, and the almost constant intensity vs the transferred momentum with &sgr; polarization. This behavior is quite different from Cu L3 edge RIXS giving a strongly dispersing bimagnon tending to zero at the center of the Brillouin zone. This is clearly shown by RIXS measurements at the Cu L3 edge that we present. The Cu L3 bimagnon spectra and those at the Cu K edge--both from the literature and from our data--however, have the same shape. These similarities and differences are understood in terms of different sampling of the bimagnon continuum. This panorama points out the unique possibilities offered by O K RIXS in the study of magnetic excitations in cuprates near the center of the BZ. [ABSTRACT FROM AUTHOR]

We present RIXS data at the O K edge from La2-xSrxCuO4 vs doping between x =0.10 and x = 0.22 with attention to the magnetic excitations in the mid-infrared region. The sampling done by RIXS is the same as in the uiidoped cuprates provided the excitation is at the first prepeak induced by doping. Note that this excitation energy is about 1.5 eV lower than that needed to see bimagnons in the parent compound. This approach allows the study of the upper region of the bimagnon continuum around 450 meV within about one third of the Brillouin zone around &Ggr;. The results show the presence of damped bimagnons and of higher even order spin excitations with almost constant spectral weight at all the dopings explored here. The implications for high-Tc studies are briefly addressed. [ABSTRACT FROM AUTHOR]

The cuprate high temperature superconductors exhibit a pronounced trend in which the superconducting transition temperature Tc increases with the number of CuC2planes n in the crystal structure. We compare the magnetic excitation spectrum of Bi2+xSr2-xCuO6+δ (Bi-2201) and Bi2Sr2Ca2CuO10+δ (Bi-2223), with n = 1 and 3, respectively, using Cu L3-edge resonant inelastic x-ray scattering. Near the antinodal zone boundary we find the paramagnon energy in Bi-2223 is substantially higher than that in Bi-2201, indicating that multilayer cuprates host stronger effective magnetic exchange interactions, providing a possible explanation for the Tc vs n scaling. In contrast, the nodal direction exhibits very strongly damped, almost nondispersive excitations. We argue that this implies that the magnetism in the doped cuprates is partially itinerant in nature. [ABSTRACT FROM AUTHOR]

Oxygen Is → 2p (K-edge) x-ray absorption spectra mimic the density of metalliclike states of transition metal oxides, thus shedding light on the electronic band structure near Fermi energies of these compounds. We take here advantage of x-ray linear dichroism measurements at the O K edge of different (SrMn03)3(LaMn03)2n superlattices, of SrMnO3 and of LaMn03 thin films. X-ray linear dichroism, in the pre-edge region of the spectra, provides evidence about the specific symmetry of the Mn 3d orbitals hybridized with the oxygen ions, thus allowing us to disentangle the pure interface contribution from those related to strain effect and charge leakage among the superlattices' constituent blocks. [ABSTRACT FROM AUTHOR]

The hole distribution in Sr14Cu24CX41 is studied by low-temperature polarization-dependent O K near-edge x-ray absorption fine-structure measurements and state-of-the-art electronic structure calculations that include core-hole and correlation effects in a mean-field approach. Contrary to all previous analysis, based on semiempirical models, we show that correlations and antiferromagnetic ordering favor the strong chain-hole attraction. For the remaining small number of holes accommodated on ladders, leg sites are preferred to rung sites. The small hole affinity of rung sites explains naturally the one-dimensional to two-dimensional crossover in the phase diagram of (La,Y,Sr,Ca)14Cu24041. [ABSTRACT FROM AUTHOR]