We probe the collective magnetic modes of La2CuO4 and underdoped La2-xSrxCuO4 (LSCO) by momentum resolved resonant inelastic x-ray scattering (RIXS) at the Cu L3 edge. For the undoped antiferromagnetic sample, we show that the single magnon dispersion measured with RIXS coincides with the one determined by inelastic neutron scattering, thus demonstrating that x rays are an alternative to neutrons in this field. In the spin dynamics of LSCO, we find a branch dispersing up to approximately 400 meV coexisting with one at lower energy. The high-energy branch has never been seen before. It indicates that underdoped LSCO is in a dynamic inhomogeneous spin state.

In 2004, Ohtomo and Hwang discovered that an electron gas is created at the interface between insulating LaAlO3 and SrTiO3 compounds. Here we show that the generation of a conducting electron gas is related to an orbital reconstruction occurring at the LaAlO3/SrTiO3 interface. Our results are based on extensive investigations of the electronic properties and of the orbital structure of the interface using x-ray absorption spectroscopy. In particular, we find that the degeneracy of the Ti 3d states is fully removed and that the Ti 3d xy levels become the first available states for conducting electrons.

The metal–insulator transition and the intriguing physical properties of rare-earth perovskite nickelates have attracted considerable attention in recent years. Nonetheless, a complete understanding of these materials remains elusive. Here we combine X-ray absorption and resonant inelastic X-ray scattering (RIXS) spectroscopies to resolve important aspects of the complex electronic structure of rare-earth nickelates, taking NdNiO3 thin film as representative example. The unusual coexistence of bound and continuum excitations observed in the RIXS spectra provides strong evidence for abundant oxygen holes in the ground state of these materials. Using cluster calculations and Anderson impurity model interpretation, we show that distinct spectral signatures arise from a Ni 3d8 configuration along with holes in the oxygen 2p valence band, confirming suggestions that these materials do not obey a conventional positive charge-transfer picture, but instead exhibit a negative charge-transfer energy in line with recent models interpreting the metal–insulator transition in terms of bond disproportionation.

By resonant inelastic x-ray scattering in the soft x-ray regime we probe the dynamical multiple-spin correlations in the antiferromagnetic cuprates La2CuO4 and CaCuO2. High resolution measurements at the copper L3 edge allow the clear observation of dispersing bimagnon excitations. Theory based on the ultrashort core-hole lifetime expansion fits the data on these coherent spin excitations without free parameters.

Linear dichroism (LD) in x -ray absorption, diffraction, transport and magnetization measurements on thin La 0.7 Sr 0.3 MnO 3 films grown on different substrates, allow identification of a peculiar interface effect, related just to the presence of the interface. We report the LD signature of preferential 3d-e g (3z 2 -r 2 ) occupation at the interface, suppressing the double exchange mechanism.This surface orbital reconstruction is opposite to that favored by residual strain and is independent of dipolar fields, the chemical nature of the substrate and the presence of capping layers.Interfaces between perovskite oxides display unexpected properties. The roles of chemistry, polarization and strain may be singled out by selective experiments, e.g.Ref.[11], where an engineered interface obtained by intercalating two LMO unit cells (u.c.) between the LSMO and the STO has been shown to recover the LSMO bulk properties even at room temperature. The role of strain on preferential orbital occupation in transition metal oxides has been widely studied [12]. The anisotropy of d-orbitals influences the electron correlation effects in an orbital direction-dependent manner, thus giving rise to the anisotropy of the electron-transfer and eventually destroying the DE order of unstrained half-metallic LSMO (Fig.1, center). The strain effect on orbital physics can be understood on the basis of the experimental phase diagram proposedby Konishi et al.,[ 13] and explained theoretically by Fang et al.[14]. Spin ordering in strained manganite is influenced by orbital ordering and several anti-ferromagnetic (AF) insulating JahnTeller distorted phases are observed: the strain induced elongation or compression of the MnO 6 octahedra leads to crystal field splitting of the e g levels, lowering either i) the (3z 2 -r 2 ) state which favors the C -type AF structure (Fig.1, left) or ii) the (x 2 -y 2 ) state which stabilizes the A -type structure ( Fig.1, right resonant transition. Polarization effects arise when the polarization vector is set parallel to t he c crystallographic axis or perpendicular to it (I c and I ab respectively). The LD is the difference between the two spectra (I ab -I c ) and gives a direct insight of the empty Mn 3dstates: a LD which is on average positive (negative) indicates a majority o f off-plane (in-plane) empty 3d states. Considering the crystal field splitting, the effect can be mainly related to the occupation of the two e g states (3r 2 -z 2 and x 2 -y 2 ) with majority spin: a LD which is on average positive (negative) is due to a preferential occupation of the in-plane x 2 -y 2 (out-of-plane 3r 2 -z 2 )orbital.Magnetization measurements were carried out by a SQUID magnetometer. Further experimental details are given in ref.[16] and [26].In Fig.2 Fig.4(b), revealing opposite signs for these two cases.Although the comparison with experiments can only be qualitative and a proper fit is not feasible, the sign reversal is observed in the experimental spectra of Fig.4(a) for energies above the E˜644 ...

Because of a typing error, the paragraph starting on page 2, line 43 should read: ''The LD is the difference between the two spectra (I ab =I c ) and gives a direct insight of the empty Mn 3d states: a LD which is on average negative (positive) indicates a majority of off-plane (in-plane) empty 3d states. Considering the crystal field splitting, the effect can be mainly related to the occupation of the two e g states (3r 2 À z 2 and x 2 À y 2 ) with majority spin: a LD which is on average negative (positive) is due to a preferential occupation of the in-plane x 2 À y 2 (out-of-plane 3r 2 À z 2 ) orbital. '' PRL 103, 079902 (2009)

We have performed x-ray linear and circular magnetic dichroism experiments at the Mn L 2,3 -edge of the La 0.7 Sr 0.3 MnO 3 ultra thin films. Our measurements show that the antiferromagnetic (AF) insulating phase is stabilized by the interfacial rearrangement of the Mn 3d orbitals, despite the relevant magnetostriction anisotropic effect on the double-exchange ferromagnetic (FM) metallic phase. As a consequence, the Mn atomic magnetic moment orientation and how it reacts to strain differ in the FM and AF phases. In some cases a FM insulating (FMI) phase adds to the AF and FM. Its peculiar magnetic properties include in-plane magnetic anisotropy and partial release of the orbital moment quenching. Nevertheless the FMI phase appears little coupled to the other ones.

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