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We used resonant inelastic x-ray scattering (RIXS) with and without analysis of the scattered photon polarization, to study dispersive spin excitations in the high temperature superconductor YBa≤sub>2≤/sub>Cu≤sub>3≤/sub>O≤sub>6+x≤/sub> over a wide range of doping levels (0.1 ≤ x ≤ 1). The excitation profiles were carefully monitored as the incident photon energy was detuned from the resonant condition, and the spin excitation energy was found to be independent of detuning for all x. These findings demonstrate that the largest fraction of the spin-flip RIXS profiles in doped cuprates arises from magnetic collective modes, rather than from incoherent particle-hole excitations as recently suggested theoretically [Benjamin et al. Phys. Rev. Lett. 112, 247002 (2014)]. Implications for the theoretical description of the electron system in the cuprates are discussed. [ABSTRACT FROM AUTHOR]

We use polarized Raman scattering to probe lattice vibrations and charge ordering in 12 nm thick, epitaxially strained PrNiO3 films, and in superlattices of PrNiO3 with the band insulator PrAlO3. A carefully adjusted confocal geometry is used to eliminate the substrate contribution to the Raman spectra. In films and superlattices under tensile strain which undergo a metal-insulator transition upon cooling, the Raman spectra reveal phonon modes characteristic of charge ordering. These anomalous phonons do not appear in compressively strained films, which remain metallic at all temperatures. For superlattices under compressive strain, the Raman spectra show no evidence of anomalous phonons indicative of charge ordering, while complementary resonant x-ray scattering experiments reveal antiferromagnetic order associated with a modest increase in resistivity upon cooling. This confirms theoretical predictions of a spin density wave phase driven by spatial confinement of the conduction electrons. [ABSTRACT FROM AUTHOR]

Using resonant inelastic x-ray scattering (RIXS) at the Cu L-absorption edge, we have observed intense, dispersive spin excitations in highly overdoped Tl2Ba2CuO6+δ (superconducting Tc = 6 K), a model compound whose normal-state charge transport and thermodynamic properties have been shown to exhibit canonical Fermi-liquid behavior. Complementary RIXS experiments on slightly overdoped Tl2Ba2CuO6+δ (Tc = 89 K) and on Y1-xCaxBa2Cu3O6+δ compounds spanning a wide range of doping levels indicate that these excitations exhibit energies and energy-integrated spectral weights closely similar to those of antiferromagnetic magnons in undoped cuprates, indicating the persistence of substantial antiferromagnetic spin correlations over a wide doping range. The surprising coexistence of such correlations with Fermi-liquid-like charge excitations in highly overdoped cuprates poses a challenge to current theoretical models of correlated-electron metals. [ABSTRACT FROM AUTHOR]

The energy of magnetic and orbital excitations of copper-oxide systems have been assessed in bulk materials, but little is known about how they change in thin films or heterostructures. Although in these samples the epitaxial strain is known to alter important physical properties, such as Tc, the actual relation to fundamental excitations remains to be established. Here we determine how the magnetic interactions and orbital splitting scale with lattice constant under strain in the prototypical insulating cuprate CaCuCO2 . We extract the scaling power laws both experimentally, using Cu L3 resonant inelastic x-ray scattering, and theoretically, with ab initio quantum chemical calculations. This combined approach quantifies the large impact of small lattice variations on the magnetic and orbital energy scales and opens the way to the production of strain-engineered samples. [ABSTRACT FROM AUTHOR]

We here report on the occurrence of strong orbital order driven by off-stoichiometry in oxide manganite films. Multiple-electronic-valence Mn ions are possibly substituted into the perovskite atomic A site (namely, A-site manganites). By combining state-of-the-art synchrotron ultrafine spectroscopies, we did provide evidence of a high ferromagnetic metallic state together with a strong orbital order of Mn ions, despite that the kinetic energy of the free charge carriers should prevent long-range orbital order. By varying the total amount of Mn ions at the perovskite A site, a specific orbital order (either in-plane or out-of-plane) can be determined. [ABSTRACT FROM AUTHOR]

Using high-resolution resonant inelastic x-ray scattering (RIXS) excited at the Cu L3 edge we have investigated the ligand field (dd) and magnetic excitations in (CaCuO2)n/(SrTiO3)n superlattices (n = 2,3) and compared them to those of a 14-nm-thick CaCuO2 film. The dd excitation spectrum reveals a pyramidal coordination of Cu ions at the CaCuO2/SrTiO3 interfaces. In the three samples, spin excitations are in the form of dispersing magnons, with similar spectral intensity but reduced dynamics in SLs with respect to pure CaCuO2. By fitting the dispersions within linear spin wave theory we have obtained the leading term of the in-plane superexchange parameters: J = 127 meV, 138 meV, and 157 meV for n = 2, 3 SLs, and CaCuO2, respectively. These results demonstrate that the anfiferromagnetic order is preserved in these SLs down to very small cuprate layer thickness and despite the chemical and structural alterations at the interface. This finding opens the way to the production of artificial Cu-based high-temperature superconductors where the charge reservoir layer is constituted by the interface itself. [ABSTRACT FROM AUTHOR]

The asymmetry between electron and hole doping in high critical-temperature superconducting (HTS) cuprates is key information for the understanding of Cooper pair formation mechanisms. Despite intensive studies on different cuprates, a comprehensive description of related magnetic and charge excitations is still fragmentary. In the present work, artificial cuprates were used to cover the entire phase diagram within the same HTS family. In particular, Cu L3-edge resonant inelastic x-ray scattering (RIXS) measurements were performed on artificial n- and p-type infinite layer (IL) epitaxial films. Beside several similarities, RIXS spectra show noticeable differences in the evolution, with doping level, of magnetic and charge intensity and damping. Compatible trends can be found in spectra measured on bulk cuprates, as well as in theoretical calculations of the spin dynamical structure factor S(q,ω). The findings give a deeper insight into the evolution of collective excitations across the cuprate phase diagram, and on underlying general features, only connected to the doping type. Moreover, they pave the way to the exploration of general properties of HTS physics over a broad range of conditions, by means of artificial compounds not constrained by the thermodynamic limitations governing the chemical stability of bulk materials. [ABSTRACT FROM AUTHOR]

Spin excitations in the overdoped high temperature superconductors Tl2Ba2CuO6+δ and (Bi,Pb)2(Sr,La)2CuO6+δ were investigated by resonant inelastic x-ray scattering (RIXS) as functions of doping and detuning of the incoming photon energy above the Cu-L3 absorption peak. The RIXS spectra at optimal doping are dominated by a paramagnon feature with peak energy independent of photon energy, similar to prior results on underdoped cuprates. Beyond optimal doping, the RIXS data indicate a sharp crossover to a regime with a strong contribution from incoherent particle-hole excitations whose maximum shows a fluorescencelike shift upon detuning. The spectra of both compound families are closely similar, and their salient features are reproduced by exact-diagonalization calculations of the single-band Hubbard model on a finite cluster. The results are discussed in the light of recent transport experiments indicating a quantum phase transition near optimal doping. [ABSTRACT FROM AUTHOR]

The charge and spin correlations in La1.875Ba0.125CuO4 (LBCO 1/8) are studied using Cu L3 edge resonant inelastic x-ray scattering (RIIXS). The static charge order (CO) is observed at a wave vector of (0.24,0) and its charge nature confirmed by measuring the dependence of this peak on the incident x-ray polarization. The damped spin excitation or "paramagnon" in LBCO 1/8 is then measured as it disperses through the CO wave vector. Within the experimental uncertainty no changes are observed in the paramagnon at that wave vector and the paramagnon seems to be similar to that measured in other cuprates, which have no static CO. Given that the stripe correlation modulates both the charge and spin degrees of freedom, it is likely that subtle changes do occur in the paramagnon due to CO. Consequently, we propose that future RIXS measurements, realized with higher-energy resolution and sensitivity, should be performed to test for these effects. [ABSTRACT FROM AUTHOR]

We report the results of a comprehensive study of charge-density wave (CDW) correlations in untwinned YBa2Cu3O6+x single crystals with 0.4 ⩽ x ⩽ 0.99 using Cu L3 edge resonant x-ray scattering (RXS). Evidence of CDW formation is found for 0.45 ⩽ x ⩽ 0.93 (hole-doping levels 0.086 ≲ p ≲ 0.163), but not for samples with x ⩽ 0.44 (p ≲ 0.084) that exhibit incommensurate spin-density-wave order, and in slightly overdoped samples with x = 0.99 (p ∼ 0.19). This suggests the presence of two proximate zero-temperature CDW critical points at Pc1 ∼ 0.08 and pc2 ∼ 0.18. Remarkably, pc2 is close to the doping level that is optimal for superconductivity. The CDW reflections are observed at incommensurate in-plane wave vectors (δa, 0) and (0, δb) with δa < δa. Both δa and δb decrease linearly with increasing doping, in agreement with recent reports on Bi-based high-Tc; superconductors, but in sharp contrast to the behavior of the La2-x (Ba,Sr)xCuO4 family. The CDW intensity and correlation length exhibit maxima at p ∼ 0.12, coincident with a plateau in the superconducting transition temperature Tc. The onset temperature of the CDW reflections depends nonmonotonically on p , with a maximum of ∼160 K for p ∼ 0.12. The RXS reflections exhibit a uniaxial intensity anisotropy. Whereas in strongly underdoped samples the reflections at (δa, 0) are much weaker than those at (0, δb), the anisotropy is minimal for p ∼ 0.12, and reversed close to optimal doping. We further observe a depression of CDW correlations upon cooling below Tc, and (for samples with p ⩾ 0.09) an enhancement of the signal when an external magnetic field up to 6 T is applied in the superconducting state. For samples with p ∼ 0.08, where prior work has revealed a field-enhancement of incommensurate magnetic order, the RXS signal is field independent. This supports a previously suggested scenario in which incommensurate charge and spin orders compete against each other, in addition to individually competing against superconductivity [Blanco-Canosa et al., Phys. Rev. Lett. 110, 187001 (2013)]. We discuss the relationship of these results to prior observations of "stripe" order in La2-x(Ba,Sr)xCuO4 , the "pseudogap" phenomenon, superconducting fluctuations, and quantum oscillations, as well as their implications for the mechanism of high-temperature superconductivity. [ABSTRACT FROM AUTHOR]

The nature of the electronic ground state of Ba2IrO4 has been addressed using soft x-ray absorption and inelastic scattering techniques in the vicinity of the oxygen K edge. From the polarization and angular dependence of x-ray absorption spectroscopy (XAS) we deduce an approximately equal superposition of xy, yz, and zx Ir4+ 5d orbitals. By combining the measured orbital occupancies, with the value of the spin-orbit coupling provided by resonant inelastic x-ray scattering (RIXS), we estimate the crystal field splitting associated with the tetragonal distortion of the IrO6 octahedra to be small, Δ≈50(50) meV. We thus conclude definitively that Ba2IrO4 is a close realization of a spin-orbit Mott insulator with a jeff=½ ground state, thereby overcoming ambiguities in this assignment associated with the interpretation of x-ray resonant scattering experiments. [ABSTRACT FROM AUTHOR]

Possible ferromagnetism induced in otherwise nonmagnetic materials has been motivating intense research in complex oxide heterostructures. Here we show that a confined magnetism is realized at the interface between SrTiO3 and two insulating polar oxides, BiMnO3 and LaAlO3. By using polarization dependent x-ray absorption spectroscopy, we find that in both cases the magnetism can be stabilized by a negative exchange interaction between the electrons transferred to the interface and local magnetic moments. These local magnetic moments are associated with magnetic Ti3+ ions at the interface itself for LaAlO3/SrTiO3 and to Mn3+ ions in the overlayer for BiMnO3/SrTiO3. In LaAlO3/SrTiO3 the induced magnetism is quenched by annealing in oxygen, suggesting a decisive role of oxygen vacancies in this phenomenon. [ABSTRACT FROM AUTHOR]

We use resonant x-ray scattering to determine the momentum-dependent charge correlations in YBa2Cu3O6.55 samples with highly ordered chain arrays of oxygen acceptors (ortho-H structure). The results reveal nearly critical, biaxial charge density wave (CDW) correlations at in-plane wave vectors (0.315, 0) and (0, 0.325). The corresponding scattering intensity exhibits a strong uniaxial anisotropy. The CDW amplitude and correlation length are enhanced as superconductivity is weakened by an external magnetic field. Analogous experiments are carried out on a YBa2Cu3O6.6 crystal with a dilute concentration of spinless (Zn) impurities, which had earlier been shown to nucleate incommensurate magnetic order. Compared to pristine crystals with the same doping level, the CDW amplitude and correlation length are found to be strongly reduced. These results indicate a three-phase competition between spin-modulated, charge-modulated, and superconducting states in underdoped YBa2Cu3O6+δ. [ABSTRACT FROM AUTHOR]

Recently, charge density wave (CDW) order in the Cu02 planes of underdoped YBa2Cu306+,5 was detected using resonant soft x-ray scattering. An important question remains: is the chain layer responsible for this charge ordering? Here, we explore the energy and polarization dependence of the resonant scattering intensity in a detwinned sample of YBa2Cu30675 with ortho-Ill oxygen ordering in the chain layer. We show that the ortho-Ill CDW order in the chains is distinct from the CDW order in the planes. The ortho-Ill structure gives rise to a commensurate superlattice reflection at Q = [0.33 0L] whose energy and polarization dependence agrees with expectations for oxygen ordering and a spatial modulation of the Cu valence in the chains. Incommensurate peaks at [0.30 0 L] and [0 0.30 L] from the CDW order in the planes are shown to be distinct in Q as well as their temperature, energy, and polarization dependence, and are thus unrelated to the structure of the chain layer. Moreover, the energy dependence of the CDW order in the planes is shown to result from a spatial modulation of energies of the Cu 2p to 3dx2_y2 transition, similar to stripe-ordered 214 cuprates. [ABSTRACT FROM AUTHOR]

We report the occurrence of superconductivity, with maximum Tc = 40 K, in superlattices (SLs) based on two insulating oxides, namely CaCuO 2 and SrTiO 3/sub>. In these (CaCuO2)n/(SrTiOsub>3)m SLs, the CuO2 planes belong only to CaCuO2 lock, which is an antiferromagnetic insulator. Superconductivity, confined within a few unit cells at the CaCuO2/SrTi O3 interface, shows up only when the SLs are grown in a highly oxidizing atmosphere, because of extra oxygen ions entering at the interfaces. The hole doping is obtained by charge transfer from the interface layers, which thus act as charge reservoir. [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 report a comprehensive Cu L3-edge resonant x-ray scattering (RXS) study of two- and three-dimensional (2D and 3D) incommensurate charge correlations in single crystals of the underdoped high-temperature superconductor YBa2Cu3O6.67 under uniaxial compression up to 1% along the two inequivalent Cu─O─Cu bond directions (a and b) in the CuO2 planes. We confirm the strong in-plane anisotropy of the 2D charge correlations and observe their symmetric response to pressure: pressure along a enhances correlations along b, and vice versa. Our results imply that the underlying order parameter is uniaxial. In contrast, 3D long-range charge order is only observed along b in response to compression along a. Spectroscopic RXS measurements show that the 3D charge order resides exclusively in the CuO2 planes and may thus be generic to the cuprates. We discuss implications of these results for models of electronic nematicity and for the interplay between charge order and superconductivity. [ABSTRACT FROM AUTHOR]

We have measured the doping and temperature dependence of lattice vibrations and magnetic excitations in the prototypical doped spin-orbit Mott insulator Sr2-xLaxIrO4 (x = 0, 0.015, and 0.10). Our findings show that the pseudospin-lattice coupling--responsible for the renormalization of several low energy phonon modes--is preserved even when long-range magnetic order is suppressed by doping. In our most highly doped sample, the single magnon (Γ point) excitation disappears while the two-magnon mode softens and becomes heavily damped. Doping-induced electron-phonon coupling is also observed in a higher energy phonon mode. We observe two different electron-phonon interaction channels, which provide evidence of the coexistence of fluctuating magnetic moments and mobile carriers in doped iridates. [ABSTRACT FROM AUTHOR]

Resonant x-ray scattering at the Dy M5 and Ni L3 absorption edges was used to probe the temperature and magnetic field dependence of magnetic order in epitaxial LaNiO3-DyScO3 superlattices. For superlattices with 2 unit cell thick LaNiO3 layers, a commensurate spiral state develops in the Ni spin system below 100 K. Upon cooling below Tind=18 K, Dy-Ni exchange interactions across the LaNiO3-DyScO3 interfaces induce collinear magnetic order of interfacial Dy moments as well as a reorientation of the Ni spins to a direction dictated by the strong magnetocrystalline anisotropy of Dy. This transition is reversible by an external magnetic field of 3 T. Tailored exchange interactions between rare-earth and transition-metal ions thus open up new perspectives for the manipulation of spin structures in metal-oxide heterostructures and devices. [ABSTRACT FROM AUTHOR]

Using Raman spectroscopy to study the correlated 4d-electron metal Sr&#95;{2}RhO&#95;{4}, we observe pronounced excitations at 220 meV and 240 meV with A&#95;{1g} and B&#95;{1g} symmetries, respectively. We identify them as transitions between the spin-orbit multiplets of the Rh ions, in close analogy to the spin-orbit excitons in the Mott insulators Sr&#95;{2}IrO&#95;{4} and α-RuCl&#95;{3}. This observation provides direct evidence for the unquenched spin-orbit coupling in Sr&#95;{2}RhO&#95;{4}. A quantitative analysis of the data reveals that the tetragonal crystal field Δ in Sr&#95;{2}RhO&#95;{4} has a sign opposite to that in insulating Sr&#95;{2}IrO&#95;{4}, which enhances the planar xy orbital character of the effective J=1/2 wave function. This supports a metallic ground state, and suggests that c-axis compression of Sr&#95;{2}RhO&#95;{4} may transform it into a quasi-two-dimensional antiferromagnetic insulator.

We use resonant inelastic x-ray scattering to probe the propagation of plasmons in the electron-doped cuprate superconductor Sr&#95;{0.9}La&#95;{0.1}CuO&#95;{2}. We detect a plasmon gap of ∼120  meV at the two-dimensional Brillouin zone center, indicating that low-energy plasmons in Sr&#95;{0.9}La&#95;{0.1}CuO&#95;{2} are not strictly acoustic. The plasmon dispersion, including the gap, is accurately captured by layered t-J-V model calculations. A similar analysis performed on recent resonant inelastic x-ray scattering data from other cuprates suggests that the plasmon gap is generic and its size is related to the magnitude of the interlayer hopping t&#95;{z}. Our work signifies the three dimensionality of the charge dynamics in layered cuprates and provides a new method to determine t&#95;{z}.

We report a comprehensive Cu L&#95;{3}-edge resonant x-ray scattering (RXS) study of two- and three-dimensional (2D and 3D) incommensurate charge correlations in single crystals of the underdoped high-temperature superconductor YBa&#95;{2}Cu&#95;{3}O&#95;{6.67} under uniaxial compression up to 1% along the two inequivalent Cu─O─Cu bond directions (a and b) in the CuO&#95;{2} planes. We confirm the strong in-plane anisotropy of the 2D charge correlations and observe their symmetric response to pressure: pressure along a enhances correlations along b, and vice versa. Our results imply that the underlying order parameter is uniaxial. In contrast, 3D long-range charge order is only observed along b in response to compression along a. Spectroscopic RXS measurements show that the 3D charge order resides exclusively in the CuO&#95;{2} planes and may thus be generic to the cuprates. We discuss implications of these results for models of electronic nematicity and for the interplay between charge order and superconductivity.

Possible ferromagnetism induced in otherwise nonmagnetic materials has been motivating intense research in complex oxide heterostructures. Here we show that a confined magnetism is realized at the interface between SrTiO3 and two insulating polar oxides, BiMnO3 and LaAlO3. By using polarization dependent x-ray absorption spectroscopy, we find that in both cases the magnetism can be stabilized by a negative exchange interaction between the electrons transferred to the interface and local magnetic moments. These local magnetic moments are associated with magnetic Ti3+ ions at the interface itself for LaAlO3/SrTiO3 and to Mn3+ ions in the overlayer for BiMnO3/SrTiO3. In LaAlO3/SrTiO3 the induced magnetism is quenched by annealing in oxygen, suggesting a decisive role of oxygen vacancies in this phenomenon.

We use resonant x-ray scattering to determine the momentum-dependent charge correlations in YBa(2)Cu(3) O(6.55) samples with highly ordered chain arrays of oxygen acceptors (ortho-II structure). The results reveal nearly critical, biaxial charge density wave (CDW) correlations at in-plane wave vectors (0.315, 0) and (0, 0.325). The corresponding scattering intensity exhibits a strong uniaxial anisotropy. The CDW amplitude and correlation length are enhanced as superconductivity is weakened by an external magnetic field. Analogous experiments are carried out on a YBa(2)Cu(3)O(6.6) crystal with a dilute concentration of spinless (Zn) impurities, which had earlier been shown to nucleate incommensurate magnetic order. Compared to pristine crystals with the same doping level, the CDW amplitude and correlation length are found to be strongly reduced. These results indicate a three-phase competition between spin-modulated, charge-modulated, and superconducting states in underdoped YBa(2)Cu(3)O(6+δ).