Multiple double-exchange mechanism by Mn2+^{2+}-doping in manganite compounds

Double-exchange mechanisms in RE$_{1-x}$AE$_{x}$MnO$_{3}$ manganites (where RE is a trivalent rare-earth ion and AE is a divalent alkali-earth ion) relies on the strong exchange interaction between two Mn$^{3+}$ and Mn$^{4+}$ ions through interfiling oxygen 2p states. Nevertheless, the role of RE and AE ions has ever been considered "silent" with respect to the DE conducting mechanisms. Here we show that a new path for DE-mechanism is indeed possible by partially replacing the RE-AE elements by Mn$^{2+}$-ions, in La-deficient La$_{x}$MnO$_{3-\delta}$ thin films. X-ray absorption spectroscopy demonstrated the relevant presence of Mn$^{2+}$ ions, which is unambiguously proved to be substituted at La-site by Resonant Inelastic X-ray Scattering. Mn$^{2+}$ is proved to be directly correlated to the enhanced magneto-transport properties because of an additional hopping mechanism trough interfiling Mn$^{2+}$-ions, theoretically confirmed by calculations within the effective single band model. The very idea to use Mn$^{2+}$ both as a doping element and an ions electronically involved in the conduction mechanism, has never been foreseen, revealing a new phenomena in transport properties of manganites. More important, such a strategy might be also pursed in other strongly correlated materials.Comment: 6 pages, 5 figure

Evolution of magnetic phases and orbital occupation in (SrMnO3)n/(LaMnO3)2n superlattices

The magnetic and electronic modifications induced at the interfaces in (SrMnO$_{3}$)$_{n}$/(LaMnO$_{3}$)$_{2n}$ superlattices have been investigated by linear and circular magnetic dichroism in the Mn L$_{2,3}$ x-ray absorption spectra. Together with theoretical calculations, our data demonstrate that the charge redistribution across interfaces favors in-plane ferromagnetic (FM) order and $e_{g}(x^{2}-y^{2})$ orbital occupation, in agreement with the average strain. Far from interfaces, inside LaMnO$_3$, electron localization and local strain favor antiferromagnetism (AFM) and $e_{g}(3z^{2}-r^{2})$ orbital occupation. For $n=1$ the high density of interfacial planes ultimately leads to dominant FM order forcing the residual AFM phase to be in-plane too, while for $n \geq 5$ the FM layers are separated by AFM regions having out-of-plane spin orientation.Comment: accepted for publication as a Rapid Communication in Physical Review

Gapped collective charge excitations and interlayer hopping in cuprate superconductors

We use resonant inelastic x-ray scattering (RIXS) to probe the propagation of plasmons in the electron-doped cuprate superconductor Sr$_{0.9}$La$_{0.1}$CuO$_2$ (SLCO). We detect a plasmon gap of $\sim$~120 meV at the two-dimensional Brillouin zone center, indicating that low-energy plasmons in SLCO 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 RIXS data from other cuprates suggests that the plasmon gap is generic and its size is related to the magnitude of the interlayer hopping $t_z$. Our work signifies the three-dimensionality of the charge dynamics in layered cuprates and provides a new method to determine $t_z$.Comment: 17 pages, 10 figures, includes Supplemental Material. Accepted for publication in Physical Review Letter

Italian consensus conference on guidelines for conservative treatment on lower limb muscle injuries in athlete.

Provide the state of the art concerning (1) biology and aetiology, (2) classification, (3) clinical assessment and (4) conservative treatment of lower limb muscle injuries (MI) in athletes. Seventy international experts with different medical backgrounds participated in the consensus conference. They discussed and approved a consensus composed of four sections which are presented in these documents. This paper represents a synthesis of the consensus conference, the following four sections are discussed: (i) The biology and aetiology of MIs. A definition of MI was formulated and some key points concerning physiology and pathogenesis of MIs were discussed. (ii) The MI classification. A classification of MIs was proposed. (iii) The MI clinical assessment, in which were discussed anamnesis, inspection and clinical examination and are provided the relative guidelines. (iv) The MI conservative treatment, in which are provided the guidelines for conservative treatment based on the severity of the lesion. Furthermore, instrumental therapy and pharmacological treatment were discussed. Knowledge of the aetiology and biology of MIs is an essential prerequisite in order to plan and conduct a rehabilitation plan. Another important aspect is the use of a rational MI classification on prognostic values. We propose a classification based on radiological investigations performed by ultrasonography and MRI strongly linked to prognostic factors. Furthermore, the consensus conference results will able to provide fundamental guidelines for diagnostic and rehabilitation practice, also considering instrumental therapy and pharmacological treatment of MI. Expert opinion, level IV

Italian consensus conference on guidelines for conservative treatment on lower limb muscle injuries in athlete

Provide the state of the art concerning (1) biology and aetiology, (2) classification, (3) clinical assessment and (4) conservative treatment of lower limb muscle injuries (MI) in athletes. Seventy international experts with different medical backgrounds participated in the consensus conference. They discussed and approved a consensus composed of four sections which are presented in these documents. This paper represents a synthesis of the consensus conference, the following four sections are discussed: (i) The biology and aetiology of MIs. A definition of MI was formulated and some key points concerning physiology and pathogenesis of MIs were discussed. (ii) The MI classification. A classification of MIs was proposed. (iii) The MI clinical assessment, in which were discussed anamnesis, inspection and clinical examination and are provided the relative guidelines. (iv) The MI conservative treatment, in which are provided the guidelines for conservative treatment based on the severity of the lesion. Furthermore, instrumental therapy and pharmacological treatment were discussed. Knowledge of the aetiology and biology of MIs is an essential prerequisite in order to plan and conduct a rehabilitation plan. Another important aspect is the use of a rational MI classification on prognostic values. We propose a classification based on radiological investigations performed by ultrasonography and MRI strongly linked to prognostic factors. Furthermore, the consensus conference results will able to provide fundamental guidelines for diagnostic and rehabilitation practice, also considering instrumental therapy and pharmacological treatment of MI. Expert opinion, level IV

Suppression of the metal-insulator transition temperature in thin La0.7Sr0.3MnO3 films

In this paper, we illustrate an approach to discriminate between epitaxial strain and other factors responsible for the decrease of the metal-insulator transition temperature (T-P) in thin La0.7Sr0.3MnO3 films grown by pulsed laser deposition. Using this approach, we have estimated the effect of the biaxial strain on T-P. Ultrathin films, independent of epitaxial strain, do not show any metal-insulator transition over the full temperature range. This finding confirms the existence of an interface dead layer. The strain-independent decrease in T-P, relative to its bulk value, observed for a much wider thickness range (up to about 1000 A) can most likely be attributed to oxygen deficiency. (C) 2004 American Institute of Physics

Ferromagnetism in ultrathin surface-free La0.7Sr0.3MnO3 layers in electrostatically defined heterostructures

Electrostatically defined perovskite oxide heterostructures, in which carriers are confined by the modulation of the A-site ion charge, offer new possibilities of tuning the magnetic properties of manganite oxides. We investigate the preferential orientation of ferromagnetic and antiferromagnetic moments in ultrathin La0.7Sr0.3MnO3 layers embedded in antiferromagnetic SrMnO3 as they undergo a metal-to-insulator transition with decreasing thickness. Our results evince the role of orbital occupation, metallicity, and competition of different magnetic phases, in absence of spurious effects occurring in thin films as a result of symmetry breaking at La0.7Sr0.3MnO3 interfaces and of incorporation of oxygen vacancies

XAS measurements and linear dichroism at the Cu L2,3 and O K edge on infinite layer e-doped superconductors

Among the cuprate superconductors, the infinite layer compound SrCuO2 is the one with the simplest crystal structure that can be electron doped (e-doped) by La substitution (Tc≈40K for x=10%). Many difficulties arise in comparing hole (h-doped) and e-doped cuprates with layered structure, as the parent compounds of the two families do not share the same crystal structure. Many differences are observed between the two families, such as different magnetic order in the undoped compounds, stronger antiferromagnetism in the e-doped, more unconventional transport properties in h-doped, different band structure. However it is not clear whether these differences are intrinsic of superconductivity in these compounds. In this respect, infinite layer compounds are interesting, due to their minimal structure, not involving (magnetic!) rare earth charge reservoir blocks of the layered compounds (such as (Nd,Ce)2CuO4). We present x-ray absorption spectroscopy (XAS) measurements at the Cu L2,3 and O K edge on (Sr,La)CuO2 thin films grown by MBE. The measurements have been performed by synchrotron radiation at the APE beamline of ELETTRA lightsource. Samples with different La and O content have been measured at different temperatures ranging from room temperature down to 30K, using linear polarized photons. Strong linear dichroism is observed at both edges, according to the square planar coordination of Cu ions. In h-doped compounds the O K pre-edge is strongly modulated with doping, as the oxygen states are influenced by the density of states at the Fermi level, thus reflecting the deployment of the upper Hubbard band into the conduction band. On the contrary no particular doping dependence is usually observed in e-doped compounds, both layered and infinite layers. However we find some pre-edge modification with La and O content of the samples. The results are interpreted in terms of hole and electron doping of the compound by either oxygen defects or La

Electronic band redistribution probed by oxygen absorption spectra of (SrMnO_{3})_{n}(LaMnO_{3})_{2n} superlattices

none10Oxygen 1s -> 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 (SrMnO3)(n)(LaMnO3)(2n) superlattices, of SrMnO3 and of LaMnO3 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.A. Galdi; C. Aruta; P. Orgiani; C. Adamo; V. Bisogni; N. B. Brookes; G. Ghiringhelli; D. G. Schlom; P. Thakur; L. MaritatoA., Galdi; C., Aruta; P., Orgiani; C., Adamo; Bisogni, Valentina; N. B., Brookes; Ghiringhelli, GIACOMO CLAUDIO; D. G., Schlom; P., Thakur; L., Maritat