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B-site ordered thin films of double perovskite Sr2CoIrO6 were epitaxially grown by a metalorganic aerosol deposition technique on various substrates, actuating different strain states. X-ray diffraction, transmission electron microscopy, and polarized far-field Raman spectroscopy confirm the strained epitaxial growth on all used substrates. Polarization-dependent Co L-2,L-3 x-ray absorption spectroscopy reveals a change of the magnetic easy axis of the antiferromagnetically ordered (high-spin) Co3+ sublattice within the strain series. By reversing the applied strain direction from tensile to compressive, the easy axis changes abruptly from in-plane to out-of-plane orientation. The low-temperature magnetoresistance changes its sign respectively and is described by a combination of weak antilocalization and anisotropic magnetoresistance effects.

We report on our investigation of the electronic structure of Ti$_2$O$_3$ using (hard) x-ray photoelectron and soft x-ray absorption spectroscopy. From the distinct satellite structures in the spectra we have been able to establish unambiguously that the Ti-Ti $c$-axis dimer in the corundum crystal structure is electronically present and forms an $a_{1g}a_{1g}$ molecular singlet in the low temperature insulating phase. Upon heating we observed a considerable spectral weight transfer to lower energies with orbital reconstruction. The insulator-metal transition may be viewed as a transition from a solid of isolated Ti-Ti molecules into a solid of electronically partially broken dimers where the Ti ions acquire additional hopping in the $a$-$b$ plane via the $e_g^{\pi}$ channel, the opening of which requires the consideration of the multiplet structure of the on-site Coulomb interaction., Comment: 7 pages, 4 figures

We have carried out a systematic experimental investigation to address the question why thin films of Fe$_3$O$_4$ (magnetite) generally have a very broad Verwey transition with lower transition temperatures as compared to the bulk. We observed using x-ray photoelectron spectroscopy, x-ray diffraction and resistivity measurements that the Verwey transition in thin films is drastically influenced not only by the oxygen stoichiometry but especially also by the substrate-induced microstructure. In particular, we found (1) that the transition temperature, the resistivity jump, and the conductivity gap of fully stoichiometric films greatly depends on the domain size, which increases gradually with increasing film thickness, (2) that the broadness of the transition scales with the width of the domain size distribution, and (3) that the hysteresis width is affected strongly by the presence of antiphase boundaries. Films grown on MgO (001) substrates showed the highest and sharpest transitions, with a 200 nm film having a T$_V$ of 122K, which is close to the bulk value. Films grown on substrates with large lattice constant mismatch revealed very broad transitions, and yet, all films show a transition with a hysteresis behavior, indicating that the transition is still first order rather than higher order., Comment: 9 pages, 12 figures

Using Co-L_(2,3) and O-K x-ray absorption spectroscopy, we reveal that the charge ordering in La_(1.5)Sr_(0.5)CoO4 involves high spin (S=3/2) Co^2+ and low spin (S=0) Co^3+ ions. This provides evidence for the spin blockade phenomenon as a source for the extremely insulating nature of the La_(2-x)Sr_(x)CoO4 series. The associated e_g^2 and e_g^0 orbital occupation accounts for the large contrast in the Co-O bond lengths, and in turn, the high charge ordering temperature. Yet, the low magnetic ordering temperature is naturally explained by the presence of the non-magnetic (S=0) Co^3+ ions. From the identification of the bands we infer that La_(1.5)Sr_(0.5)CoO4 is a narrow band material., Comment: 5 pages, 3 figures

Sr3(Ru1-xMnx)2O7, in which 4d-Ru is substituted by the more localized 3d-Mn, is studied by x-ray dichroism and spin-resolved density functional theory. We find that Mn impurities do not exhibit the same 4+ valence of Ru, but act as 3+ acceptors; the extra eg electron occupies the in-plane 3dx2-y2 orbital instead of the expected out-of-plane 3d3z2-r2. We propose that the 3d-4d interplay, via the ligand oxygen orbitals, is responsible for this crystal-field level inversion and the material's transition to an antiferromagnetic, possibly orbitally-ordered, low-temperature state., Comment: A high-resolution version can be found at http://www.physics.ubc.ca/~quantmat/ARPES/PUBLICATIONS/Articles/MnSr3Ru2O7_XAS.pdf

We compare for Ho metal the x-ray absorption spectrum and the resonant soft x-ray diffraction spectra obtained at the $3d_{5/2} \to 4f$ ($M_5$) resonance for the magnetic 1st and 2nd order diffraction peaks $(0,0,��)$ and $(0,0,2��)$ with the result of an atomic multiplet calculation. We find a good agreement between experiment and simulation giving evidence that this kind of simulation is well suited to quantitatively analyze resonant soft x-ray diffraction data from correlated electron systems.

We found that the conventional model of orbital ordering of 3x^2-r^2/3y^2-r^2 type in the eg states of La_0.5Sr_1.5MnO_4 is incompatible with measurements of linear dichroism in the Mn 2p-edge x-ray absorption, whereas these eg states exhibit predominantly cross-type orbital ordering of x^2-z^2/y^2-z^2. LDA+U band-structure calculations reveal that such a cross-type orbital ordering results from a combined effect of antiferromagnetic structure, Jahn-Teller distortion, and on-site Coulomb interactions., Comment: 5 pages, 5 figures, to be published in PRL

With on- and off- resonant excitation photons, spin-resolved Auger electron spectra of epitaxial CrO$_{2}$ thin films show an experimental evidence of the spin-selective KLL Auger decay. The on-resonance O KLL Auger electrons are found to be highly spin-polarized, while the off-resonance ones with almost zero spin polarization. These results lead to conclude that the two-hole final state in KLL Auger decay is a spin-singlet. Applications to spin-resolved absorption spectroscopy are discussed., Comment: 4 pages, 3 figures

We have measured low-temperature specific heat C(T, H) of La1.9Sr0.1Cu1-xZnxO4 (x=0, 0.01, and 0.02) both in zero and applied magnetic fields. A pronounced dip of C/T below 2 K was first observed in Zn-doped samples, which is absent in the nominally clean one. If the origin of the dip in C/T is electronic, the quasiparticle density of states N(E) in Zn-doped samples may be depressed below a small energy scale E0. The present data can be well described by the model N(E)=N(0)+alphaE^1/2, with a non-zero N(0) and positive alpha. Magnetic fields depress N(0) and lead to an increase in E0, while leaving the energy dependence of N(E) unchanged. This novel depression of N(E) below E0 in impurity-doped cuprates can not be reconciled with the semi-classical self-consistent approximation model. Discussions in the framework based on the non-linear sigma model field theory and other possible explanations are presented in this Letter.