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The new frontier for spintronics is the realization of devices in which the spin can be controlled by electric fields. Multiferroics, materials exhibiting strong interplay between spin and orbital degrees of freedom, are candidates for the realization of such a paradigm. In this work, we study the magnetoelectric coupling in epitaxial $$\hbox {BiMnO}_3$$ thin films which exhibit a large saturation magnetization. By combining X-ray absorption spectroscopy data and theoretical modeling, we demonstrate that $$\hbox {BiMnO}_3$$ thin films have an improper magnetoelectric behavior, characterized by competing antiferromagnetic and ferromagnetic correlations. As a consequence, we show that in these materials the Mn-3d orbital and magnetic orders can be tuned via the ferroelectric polarization, opening perspectives for the realization of novel spintronic devices.

Polar surfaces are known to be unstable due to the divergence of the surface electrostatic energy. Here we report on the experimental determination, by grazing incidence x-ray diffraction, of the surface structure of polar Ti-terminated (111) ${\mathrm{SrTiO}}_{3}$ single crystals. We find that the polar instability of the $1\ifmmode\times\else\texttimes\fi{}1$ surface is solved by a pure electronic reconstruction mechanism, which induces out-of-plane ionic displacements typical of the polar response of ${\mathrm{SrTiO}}_{3}$ layers to an electron confining potential. On the other hand, the surface instability can be also eliminated by a structural reconstruction driven by a change in the surface stoichiometry, which induces a variety of $3\ifmmode\times\else\texttimes\fi{}3$ (111) ${\mathrm{SrTiO}}_{3}$ surfaces consisting in an incomplete Ti (surface)--${\mathrm{O}}_{2}$ (subsurface) layer covering the $1\ifmmode\times\else\texttimes\fi{}1$ Ti-terminated (111) ${\mathrm{SrTiO}}_{3}$ truncated crystal. In both cases, the ${\mathrm{TiO}}_{6}$ octahedra are characterized by trigonal distortions affecting the structural and the electronic symmetry of several unit cells from the surface. These findings show that the stabilization of the polar (111) ${\mathrm{SrTiO}}_{3}$ surface can lead to the formation of quasi-two-dimensional electron systems characterized by radically different ground states which depend on the surface reconstructions.

Charge density waves are a common occurrence in all families of high critical temperature superconducting cuprates. Although consistently observed in the underdoped region of the phase diagram and at relatively low temperatures, it is still unclear to what extent they influence the unusual properties of these systems. Using resonant x-ray scattering we carefully determined the temperature dependence of charge density modulations in (Y,Nd)Ba$_2$Cu$_3$O$_{7-{\delta}}$ for three doping levels. We discovered short-range dynamical charge density fluctuations besides the previously known quasi-critical charge density waves. They persist up to well above the pseudogap temperature T*, are characterized by energies of few meV and pervade a large area of the phase diagram, so that they can play a key role in shaping the peculiar normal-state properties of cuprates., Comment: 34 pages, 4 figures, 11 supplementary figures

Resume La duodenopancreatectomie cephalique (DPC) est le traitement de choix pour les tumeurs malignes periampullaires, et aujourd’hui, les indications se sont elargies aux maladies benignes, telles la pancreatite chronique symptomatique, la dystrophie kystique sur pancreas aberrant de la paroi duodenale et les tumeurs papillaires benignes qui ne relevent pas de la chirurgie conservatrice. En depit d’une baisse significative de la mortalite dans les centres a gros volume pendant les trois dernieres decennies (de > 20 % dans les annees 1980 a

Charge density modulations have been observed in all families of high-critical temperature (

We report on the magnetotransport properties of a spin-polarized two-dimensional electron system (2DES) formed in LaAlO3(LAO)/EuTiO3/SrTiO3 (STO) heterostructures. We show that, at low temperature, the 2DES magnetoconductance exhibits weak antilocalization corrections related to Rashba spin-orbit scattering, in analogy with the LAO/STO 2DES. However, the characteristic spin-orbit scattering field decreases substantially for carrier density higher than 1.9×1013cm-2. We attribute this behavior to the masking effect of ferromagnetism, which sets in at the same carrier density and at a temperature below 10 K. Our work shows that, while weak antilocalization corrections to the magnetoconductance are strongly reduced by the emergence of ferromagnetism, they persist in a large part of the phase diagram of a spin-polarized oxide 2DES.

We used x-ray absorption spectroscopy to study the orbital symmetry and the energy band splitting of (111) LaAlO${_3}$/SrTiO${_3}$ and LaAlO${_3}$/EuTiO${_3}$/SrTiO${_3}$ heterostructures, hosting a quasi two-dimensional electron system (q2DES), and of a Ti-terminated (111) SrTiO${_3}$ single crystal, also known to form a q2DES at its surface. We demonstrate that the bulk tetragonal Ti-3d D${_4}$${_h}$ crystal field is turned into trigonal D${_3}$${_d}$ crystal field in all cases. The symmetry adapted a${_1}$${_g}$ and e${^\pi_g}$ orbitals are non-degenerate in energy and their splitting, \Delta, is positive at the bare STO surface but negative in the heterostructures, where the a${_1}$${_g}$ orbital is lowest in energy. These results demonstrate that the interfacial symmetry breaking induced by epitaxial engineering of oxide interfaces has a dramatic effect on their electronic properties, and it can be used to manipulate the ground state of the q2DES.

In the underdoped regime, the cuprate high-temperature superconductors exhibit a host of unusual collective phenomena, including unconventional spin and charge density modulations, Fermi surface reconstructions, and a pseudogap in various physical observables. Conversely, overdoped cuprates are generally regarded as conventional Fermi liquids possessing no collective electronic order. In partial contradiction to this widely held picture, we report resonant X-ray scattering measurements revealing incommensurate charge order reflections for overdoped (Bi,Pb)

Intercalation of 9-aminoacridine (9AA: C 13 H 10 N 2 ) in thin films of exfoliated Li 2 x − y Mn 1− x PS 3 has been performed by means of a solution approach starting from the hydrochloride salt of the organic species (9AAHCl: C 13 H 10 N 2 ·HCl). The resulting nanocomposite Li 2 x − y Mn 1− x PS 3 (C 13 H 11 N 2 ) y films have been investigated by X-ray photoemission spectroscopy (XPS), at room temperature, in the regions of the Mn, P, S and Cl 2p, Li, C and N 1s and Mn 3p core levels. The XPS analysis has been also carried out on the 9-aminoacridine hydrochloride films whose XPS spectra have been compared with those of the Li 2 x − y Mn 1− x PS 3 (C 13 H 11 N 2 ) y films to obtain information about the nature of the interaction between the guest species (9AAH + ) and the matrix (Li 2 x − y Mn 1− x PS 3 − ).

In high Tc superconductors the magnetic and electronic properties are determined by the probability that valence electrons virtually jump from site to site in the CuO2 planes, a mechanism opposed by on-site Coulomb repulsion and favored by hopping integrals. The spatial extent of the latter is related to transport properties, including superconductivity, and to the dispersion relation of spin excitations (magnons). Here, for three antiferromagnetic parent compounds (single-layer Bi2Sr0.99La1.1CuO6+delta, double-layer Nd1.2Ba1.8Cu3O6 and infinite-layer CaCuO2) differing by the number of apical atoms, we compare the magnetic spectra measured by resonant inelastic x-ray scattering over a significant portion of the reciprocal space and with unprecedented accuracy. We observe that the absence of apical oxygens increases the in-plane hopping range and, in CaCuO2, it leads to a genuine 3D exchange-bond network. These results establish a corresponding relation between the exchange interactions and the crystal structure, and provide fresh insight into the materials dependence of the superconducting transition temperature., 9 pages, 4 figures, 1 Table, 42 references

Advances in growth technology of oxide materials allow single atomic layer control of heterostructures. In particular delta doping, a key materials' engineering tool in today's semiconductor technology, is now also available for oxides. Here we show that a fully electric-field-tunable spin-polarized and superconducting quasi-2D electron system (q2DES) can be artificially created by inserting a few unit cells of delta doping EuTiO3 at the interface between LaAlO3 and SrTiO3 oxides(1,2). Spin polarization emerges below the ferromagnetic transition temperature of the EuTiO3 layer (T-FM = 6-8 K) and is due to the exchange interaction between the magnetic moments of Eu-4f and of Ti-3d electrons. Moreover, in a large region of the phase diagram, superconductivity sets in from a ferromagnetic normal state. The occurrence of magnetic interactions, superconductivity and spin-orbit coupling in the same q2DES makes the LaAlO3/EuTiO3/SrTiO3 system an intriguing platform for the emergence of novel quantum phases in low-dimensional materials.

Metal-organic framework (MOF) intercalated with conductive graphene-like (GL) layers were synthesized and characterized. The selected MOF, the copper-based HKUST-1, combines high surface area, water stability, simple preparation and low costs. GL layers used to intercalate the MOF structure were obtained by a two-step, high-controlled, oxidation/reduction wet treatment of a high surface carbon black [1,2]. MOF composites were produced at different carbonaceous layers load. Elemental analysis demonstrated a complete incorporation of the carbonaceous layers into the hybrid structure. X-ray diffraction measurements revealed patterns resembling the ones reported for pure HKUST-1, indicating that the presence of intercalated GL layers does not prevent the formation of linkages between Cu ions and the BTC molecule, leading to the formation of HKUST-1 crystals (with negligible presence of the competing CuO2 phase). The Scanning Electron Microscope observations are in agreement with such structural results. Ar adsorption/desorption isotherms showed the preservation of the microporous character of the samples with the GL intercalation, revealing however a decrease in the average size of the pores for higher concentrations [3]. Spectroscopic and electrical conductivity characterizations were performed on GL, MOF and hybrid samples. The analysis of Infrared spectra and x-ray absorption spectra suggests that the carboxylic functionalities of the graphenic layers have interacted with the Cu dimers, and chemical interactions are involved in the formation of the composites. Likely, the presence of residuals of carboxylic groups, located at the edges of the GL basal planes, helps the interaction with the MOF crystals, similarly with those observed for MOF/Graphite-Oxide composites. Once again, this seems to not interfere with the MOF crystal formation [3]. The electrical conductivity rapidly increases with the added GL percentage, ranging over 5 orders of magnitude when the GL amounts changes between 5% and 40% wt. The increase does not follow a linear behavior. The observed strongly superlinear trend vs. doping and the observation of a threshold doping can be interpreted in terms of percolation theory. The relatively large threshold and saturation values for the GL concentration suggest a weak interaction between the filler particles inside the matrices, probably due to a good dispersion triggered by the high porosity of the host material [3].

We present here the design and fabrication of conductive interfaces by an efficient integration of two materials featuring conjugate ? systems, namely the human pigment eumelanin (EU) [1] and graphene like (GL) layers [2,3]. The hybrid materials (EUGLs) exhibited adhesion, water stability, biocompatibility and improved electrical conductivity with respect to the pure pigment due to the presence of embedded GL layers [2]. EUGLs were easily produced allowing eumelanin precursors (5,6-dihydroxyindole (DHI) and/or 5,6-dihydroxyindole-2-carboxylic acid, DHICA [1]) to polymerize in a water suspension of GL layers [2]. Comparative AFM inspection of the morphologies of eumelanin, GL and EUGL thin films indicates a consistent modification induced by eumelanin to the GL self-assembling. The hybrid film has locally a more granular surface compared to the EU film. Electrical dc resistivity was measured in a standard four contacts configuration. All the curves show an ohmic behavior, but with extremely different resistance. The poor electrical conductivity (?) of EU is confirmed, while EUGL exhibited a ? value more than four orders of magnitudes greater than the one of the parent EU precursor. A time-decay of ? in the eumelanin and hybrid samples was also detected (while this phenomenon is absent in the GL film). On both EU and EUGL samples, the decay of ? seems to be composed by two contributions, exhibiting two different time scales (a clear two-scale behavior) and different quantitative amounts. The double time-scale of ? decay suggests the presence of a double contribution to the electrical transport in both eumelanin and EUGL sample: ionic and electronic. In the GL film the ionic transport (as well a huge trapping of electrons) is missing. The chemical-physical, electrical and morphological analyses indicate that the actual composition of the hybrid EUGL could be considered as the outcome of quantitative merging of the starting materials. It can be speculated that both covalent bonds and ?-? stacking are expected to be involved in EU-GL interaction. To get more insights on this issue, more sophisticated analytical techniques were employed: X-ray absorption spectroscopy with synchrotron radiation and solid state nuclear magnetic resonance. The study of the data collected is still ongoing however available evidences do suggest that electronic and structural properties are strictly interconnected. The deep understanding of structure-behavior relationship in EUGLs is crucial for expanding the scope of eumelanin in bioelectronics and paving the way to advanced biocompatible organic electrochemical transistor-like interfaces capable to translate cellular activity in electrical signals.

We measured high resolution Cu $L_3$ edge resonant inelastic x-ray scattering (RIXS) of the undoped cuprates La$_2$CuO$_4$, Sr$_2$CuO$_2$Cl$_2$, CaCuO$_2$ and NdBa$_2$Cu$_3$O$_6$. The dominant spectral features were assigned to $dd$ excitations and we extensively studied their polarization and scattering geometry dependence. In a pure ionic picture, we calculated the theoretical cross sections for those excitations and used them to fit the experimental data with excellent agreement. By doing so, we were able to determine the energy and symmetry of Cu-3$d$ states for the four systems with unprecedented accuracy and confidence. The values of the effective parameters could be obtained for the single ion crystal field model but not for a simple two-dimensional cluster model. The firm experimental assessment of $dd$ excitation energies carries important consequences for the physics of high $T_c$ superconductors. On one hand, having found that the minimum energy of orbital excitation is always $\geq 1.4$ eV, i.e., well above the mid-infrared spectral range, leaves to magnetic excitations (up to 300 meV) a major role in Cooper pairing in cuprates. On the other hand, it has become possible to study quantitatively the effective influence of $dd$ excitations on the superconducting gap in cuprates., 22 pages, 11 figures, 1 table

In this paper we report on the growth mode selection in epitaxial high critical temperature Nd1+xBa2?xCu3O7 (NdBCO) films. The samples have been deposited on (100) SrTiO3 single crystals by high oxygen pressure diode sputtering using a Nd0.97Ba2.03Cu3O7 polycrystalline target. The effect of different deposition parameters on the morphology, superconductivity and structure has been investigated by atomic force microscopy, resistivity and inductive measurements, and x-ray diffraction respectively. While the deposition temperature and oxygen pressure mainly affect the critical temperature of the samples, the surface morphology is strongly dependent on the target?substrate distance. Films realized in identical deposition conditions, i.e.?oxygen pressure, rate and substrate temperature, exhibit different growth modes associated with a 10% change of the target?substrate distance. The typical surface roughness of 110?nm thick NdBCO films deposited on SrTiO3 substrates is 1.0?nm (rms) on 5 ? 5??m2 areas. Surprisingly, the critical current density and its temperature dependence are found to be independent of the surface morphology of the films investigated, and are well described by strong pinning provided by large linear defects.

We study the structural, magnetic, and transport properties of LaAlO3/EuTiO3/SrTiO3 heterostructures grown by pulsed laser deposition. The samples are characterized in situ by electron diffraction and scanning probe microscopy and ex situ by transport measurements and x-ray absorption spectroscopy. LaAlO3/EuTiO3/SrTiO3 films show a ferromagnetic transition at T

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.

Trypanosoma cruzi isolated from 55 chronic chagasic patients were grouped into isozymic strains on the basis of electrophoretic patterns for a set of six enzymes. The total sample showed a distribution of asymptomatic (63.6%) and clinically ill (36.4%) patients similar to that generally reported for Chagas' disease. Six of the 12 zymodemes known to exist in Argentina have been isolated from humans. Only two (Z1 and Z12) are frequent and widely distributed in the endemic area. These two zymodemes differ significantly in their pathogenicity. The proportion of asymptomatic patients was higher with the Z1 zymodeme (81.1%) than with the Z12 zymodeme (27.3%). The incidence of heart alterations was lower in Z1 than in Z12 zymodeme patients (18.9% versus 72.7%). Clinically evident acute disease was seen in 36.3% of cases with zymodeme Z12 and in 8.1% of cases with zymodeme Z1. The differences between the two prevalent zymodemes in Argentina are statistically significant. These observations indicate that the Z1 T. cruzi is a more benign strain than Z12. Patients infected with Z1 would be more likely to be asymptomatic for a longer time than those infected with Z12. The risk of cardiac lesion would be greater for patients harboring Z12 T. cruzi than for those with Z1. The results suggest that strain identification could be a useful prognostic tool.

An extensive surface characterization of hydrofluoric acid (HF) etched and annealed SrTiO3 single crystals, vacuum-annealed below 300 degrees C, reveals the formation of a two-dimensional electron gas (2DEG). A joint scanning tunneling spectroscopy and low-energy electron diffraction analysis allows us to associate the surface metallic state (characterized by the presence of a nonzero density of states close to the Fermi level) with the low-temperature-annealed highly ordered 1 x 1 reconstructed SrTiO3 surface hosting two-dimensional carriers. Meanwhile, a gap opens in the tunneling spectrum of 2 x 1 reconstructed, high-temperature-annealed surfaces. X-ray photoemission spectroscopy shows that the metallic state is associated with the surface formation of Ti3+. Recently published photoemission data demonstrated the formation of a 2DEG on the surface of cleaved SrTiO3, while scanning tunneling spectroscopy on crystals heated at high temperature revealed gaplike features: Our results can help reconcile this seemingly contradicting phenomenology observed so far by scanning tunneling spectroscopy and photoemission spectroscopy.

By using scanning tunneling microscopy/spectroscopy we show that the interface between LaAlO3 and SrTiO3 band insulators is characterized by in-gap interface states. These features were observed in insulating as well as conducting LaAlO3/SrTiO3 bilayers. The data show how the interface density of states evolves across the insulating to metal transition, demonstrating that nanoscale electronic inhomogeneities in the system are induced by spatially localized electrons.

Proximity-effect and resistance magneto-fluctuations measurements in submicron Nd1.2Ba1.8Cu3Oz (NBCO) nano-loops are reported to investigate coherent charge transport in the non-superconducting state. We find an unexpected inhibition of cooper pair transport, and a destruction of the induced superconductivity, by lowering the temperature from 6K to 250mK. This effect is accompanied by a significant change in the conductance-voltage characteristics and in the zero bias conductance response to the magnetic field pointing to the activation of a strong pair breaking mechanism at lower temperature. The data are discussed in the framework of mesoscopic effects specific to superconducting nanostructures, proximity effect and high temperature superconductivity., to appear on new journal of Physics

Manganese thiophosphate powders have been intercalated with sodium ions at two different intercalation times (150 min and 180 min) in order to evaluate the influence of this parameter on the dielectric properties of the obtained compounds labeled like Na2xMn1−xPS3. In particular, dielectric permittivity measures have been carried out as a function of temperature (80 K–350 K) and frequency (20 Hz to 1 MHz) and compared with each other and with those of the pure matrix and of the Na2xMn1−xPS3 compound corresponding to a 120 min intercalation time. Both investigated compounds show a dielectric response characterized by a loss peak at low temperatures, by a strong dispersion at low frequency and at not very high temperatures and by a crossover frequency showing an Arrhenius temperature dependence in agreement with what already observed in Na2xMn1−xPS3 (120 min). The results have been also discussed in terms of ac conductivity, Maxwell–Wagner–Sillar (MWS) polarization, electrode polarization and dc conductivity and all the above cited features have been attributed to the Na+ ions which are, by their nature, hopping charge carriers that behave like jumping dipoles in their alternate motions and simultaneously show conducting characteristics resulting from their extended hopping over many sites. This attribution allows us to classify the analyzed sodium compounds like hopping charge carrier systems in which a greater Na intercalation time translates into a decrease in the loss peak intensity and an increase in the activation energy associated to the crossover frequency.

There are increasing indications that superconductivity competes with other orders in cuprate superconductors, but obtaining direct evidence with bulk-sensitive probes is challenging. We have used resonant soft x-ray scattering to identify two-dimensional charge fluctuations with an incommensurate periodicity of $\bf \sim 3.2$ lattice units in the copper-oxide planes of the superconductors (Y,Nd)Ba$_2$Cu$_3$O$_{6+x}$ with hole concentrations $0.09 \leq p \leq 0.13$ per planar Cu ion. The intensity and correlation length of the fluctuation signal increase strongly upon cooling down to the superconducting transition temperature, $T_c$; further cooling below $T_c$ abruptly reverses the divergence of the charge correlations. In combination with prior observations of a large gap in the spin excitation spectrum, these data indicate an incipient charge-density-wave instability that competes with superconductivity., Comment: to appear in Science

In the search for the mechanism of high-temperature superconductivity, intense research has been focused on the evolution of the spin excitation spectrum upon doping from the antiferromagnetic insulating to the superconducting states of the cuprates. Because of technical limitations, the experimental investigation of doped cuprates has been largely focused on low-energy excitations in a small range of momentum space. Here we use resonant inelastic x-ray scattering to show that a large family of superconductors, encompassing underdoped YBa$_2$Cu$_4$O$_8$ and overdoped YBa$_2$Cu$_3$O$_{7}$, exhibits damped spin excitations (paramagnons) with dispersions and spectral weights closely similar to those of magnons in undoped cuprates. %The results are in excellent agreement with the spin excitations obtained by exact diagonalization of the $\bf t-J$ Hamiltonian on finite-sized clusters. The comprehensive experimental description of this surprisingly simple spectrum permits quantitative tests of magnetic Cooper pairing models. A numerical solution of the Eliashberg equations for the magnetic spectrum of YBa$_2$Cu$_3$O$_{7}$ reproduces its superconducting transition temperature within a factor of two, a level of agreement comparable to Eliashberg theories of conventional superconductors., Main text (11 pages, 4 figures) + supplementary information (4 pages, 4 figures, 1 table). An updated version will appear in Nature Physics

Na 0.88 Mn 0.56 PS 3 compounds have been synthesized by starting from MnPS 3 polycrystalline powders by means of a two-step cation-exchange process at a higher intercalation time than the one used for producing the literature reported Na 0.62 Mn 0.69 PS 3 compounds. The obtained samples have been characterized by X-ray photoelectron spectroscopy (XPS). The resulting spectra of the so-synthesized compounds have been compared with those observed in Na 0.62 Mn 0.69 PS 3 in our previous paper and similar electronic properties have been noted. In particular by XPS it has been shown that greater sodium content affects neither the core-level binding energies of the host matrix elements nor the type of link between Na + and (Mn 1− x PS 3 ) − .

The appearance of high-mobility electrons at the LaAlO3/SrTiO3 interface has raised strong interest in the material science community and a lively debate on the origin of the phenomenon. A possible explanation is an electronic reconstruction, realizing a transfer of electrons to SrTiO3 at the interface, thereby avoiding the build-up of excessive Coulomb energy as described by the "polarization catastrophe" associated with the alternating polar layers of the LaAlO3 film. Theoretical models predict that electrons are transferred into titanium 3d(xy) interface states and, in the presence of strong correlations, generate a charge and orbital order. Here we provide experimental evidence that at room temperature the local density of states of the LaAlO3/SrTiO3 conducting interface is modulated at the nanoscale in a short-range quasiperiodic pattern, which is consistent with the appearance of an orbital (short-range) order. This result, together with the splitting of the 3d states, confirms that an electronic reconstruction drives the functional properties of the LaAlO3/SrTiO3 oxide interface. The short-range superstructure does not fully agree with the theoretical predictions. Thus, further experimental and theoretical investigations are required to understand the electronic properties of the 2D electron system realised at the LaAlO3/SrTiO3 interface.

SUMMARYIsolates of Trypanosoma cruzi from human patients, domestic and sylvatic animals and vector insects were obtained in different areas of Argentina. Electrophoretic patterns of enzymes from extracts of 95 isolates were analysed. On the basis of zymograms providing information on 10 loci, 12 zymodemes are described according to their genotypes. Data presented show fixed heterozygosity, absence of segregation of genotypes, significant departures from Hardy–Weinberg equilibrium, and over-represented genotypes. This evidence supports the hypothesis that sexual reproduction is very restricted or absent in this parasite. The proportion of polymorphic loci is 80%. The expected mean heterozygosity per locus (He) is 0·43, while the observed value (Ho) is 0·24. Differences between these values may be explained by accepting a basically clonal structure for T. cruzi. The data matrix of 12 zymodemes using 28 characters was analysed using a Wagner parsimony algorithm. Two equally most parsimonious unrooted trees were generated; both have 39 steps. The results show clusters clearly separated according to the geographical origin of the stocks. There are some indications of some correlations between genetic composition of the parasite and the clinical picture of the infection in human patients.

International audience; X-ray magnetic circular dichroism provides evidence of an out-of-plane spin moment in undoped and doped cuprates. In La2CuO4 this moment is related to the canting of the antiferromagnetically ordered Cu2+ spins caused by the Dzyaloshinskii-Moriya interaction within the CuO2 planes. This canting gives rise to the well-known weak ferromagnetism in high magnetic fields. We find a similar behavior in doped compounds, both in the normal and in the superconducting state, but with a different temperature dependence typical of paramagnetic systems. This result suggests that, together with short-range in-plane antiferromagnetic correlations, the Dzyaloshinskii-Moriya interaction survives up to optimal doping and in the superconducting state.

Recently it was predicted theoretically and confirmed experimentally that in cuprates single-magnon dispersions can be mapped out with resonant inelastic x-ray scattering (RIXS) at the copper ${L}_{3}$ edge. To further establish RIXS as a viable technique we investigate the momentum and incident photon polarization dependence of the single-magnon spectral weight in a variety of layered undoped antiferromagnetic compounds. The agreement of experimental and theoretical results bolsters the assignment of RIXS spectral features to single magnons. This detailed analysis allows to disentangle single-magnon scattering from other spectral contributions. Moreover, it is a necessary premise for future research aimed at investigating processes that modulate spectral weights beyond the predictions of linear spin-wave theory.

We probe the collective magnetic modes of ${\mathrm{La}}_{2}{\mathrm{CuO}}_{4}$ and underdoped ${\mathrm{La}}_{2\ensuremath{-}x}{\mathrm{Sr}}_{x}{\mathrm{CuO}}_{4}$ (LSCO) by momentum resolved resonant inelastic x-ray scattering (RIXS) at the Cu ${L}_{3}$ 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 $\ensuremath{\sim}400\text{ }\text{ }\mathrm{meV}$ 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.

The appearance of high mobility electrons at the LaAlO 3 /SrTiO 3 (LAO/STO) interface has raised strong interest in the material science community and a lively debate on the origin of the phenomenon. In particular, in view of the large band gaps of the two bulk single crystals constituting this heterostructure, the realization of a conducting system was totally unexpected. A possible explanation is an electronic reconstruction of the interface, realizing a transfer of electrons from the LaAlO 3 surface to SrTiO 3 near the interface, thereby avoiding the polarization catastrophe associated with the alternating polar layers of the LaAlO 3 film. The predictions of theoretical models based on this idea are quite peculiar and need to be verified by specific experiments able to address the electronic properties of the LAO/STO buried interface. Here, by using x-ray spectroscopy techniques, we show that the appearance of an electron system is correlated to the removal of the degeneracy of the titanium 3d states, and doped electrons appear in a band preferentially created by the hybridization between 3d xy states of titanium and oxygen 2p x,y states. This splitting is consistent with an ordering of the Ti 3d xy orbital belonging to the TiO 6 octahedra close to the interface, as theoretically proposed. However, the valence of titanium ions remains prevalently 4+, therefore other mechanisms should be also considered for the stabilization of the system.

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.

By resonant inelastic x-ray scattering in the soft x-ray regime we probe the dynamical multiple-spin correlations in the antiferromagnetic cuprates ${\mathrm{La}}_{2}{\mathrm{CuO}}_{4}$ and ${\mathrm{CaCuO}}_{2}$. High resolution measurements at the copper ${L}_{3}$ 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.

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.

A light emitting structure consisting of two coupled microcavities has been realized and studied. One of the two cavities contains a luminescent organic thin film of tetrakis (4-methoxyphenyl)porphyrin, whereas the other microcavity is a dielectric structure coupled to the organic one by means of a LiF/ZnS Bragg mirror. Reflectivity spectra show the presence of two well defined cavity dips. We observe an energy splitting of the two cavity modes. Despite the fact that only one cavity contains the active layer, the photoluminescence spectra display two peaks with comparable intensities at the same energy of the reflectivity dips. These observations indicate the strong coupling of the two cavities. The comparison of the diagonalized effective Hamiltonian with the observed resonances further confirms the strong coupling. (C) 2009 American Institute of Physics.

We study the emission properties of a high quality monolithic microcavity with an embedded ultrathin organic tetrakis(4-methoxyphenyl)porphyrin layer. Spectral and angle-resolved photoluminescence measurements show a well defined polarized doublet at detection angles larger than 15 degrees. The splitting energy ranges up to 70 meV. The usual employed mechanism, based on the mismatch between the center of the mirror stop band and the wavelength of the microcavity, accounts only for a small fraction of the observed splitting. A transfer matrix model taking into account the optical anisotropy of the organic layer, has been employed to reproduce the observed experimental results. The anisotropy of the organic layer, confirmed by optical absorption spectroscopy, origins from a local molecular order as inferred by atomic force microscopy measurements.

X-ray absorption spectroscopy in the presence of an electric field has been used to study the doping mechanism of the CuO2 planes in Nd1+xBa2-xCu3O7 compounds. The electric field effect doping is well-known as a method to modify the electrical properties of a thin film using an external gate voltage and in the copper based high critical temperature superconductors (HTS), it has been used to shift the critical temperature and even to induce phase transitions. Field effect experiments in ultra-thin HTS are usually interpreted by supposing that the induced charges develop into carriers in the CuO2 conducting planes, thus changing the filling of the Zhang-Rice (ZR) band. Here we show that the polarization charges in both insulating and superconducting films, are mainly confined in the charge reservoir, and in particular in the CuO chains. The characteristics of the charge reservoir layer determine the doping of the CuO2 planes, achieved by transfer of a fraction of the total injected charges. Moreover we found that holes injection in the CuO2 planes is reduced in oxygen deficient NdBCO films.

Sodium intercalated manganese thiophosphate Na(0.62)Mn(0.69)PS(3) powders have been synthesized by a two-step ion-exchange process. Dielectric measurements have been performed as a function of both temperature and frequency on the prepared samples in the 20-10(6) Hz frequency range over the 78-350 K temperature range by using the autobalancing bridge method. The temperature dependence of the dielectric constant imaginary part reveals the presence of a loss peak at the low temperatures together with a strong dispersion at the low frequencies and at the highest investigated temperatures. While the loss peak presence is characteristic for dipolar polarization processes, the strong low frequency dispersion at not very high temperatures, observed also in the dielectric constant real part, is typical for system with hopping charge carriers. A hypothesis about the nature of such carriers has been formulated on the basis of both the ion-exchange intercalation process and the comparison with the dielectric spectra previously observed for cesium intercalated manganese thiophosphate Na(0.46)Mn(0.77)PS(3) compounds.

We report a detailed study of the transport properties of Nd1+xBa2�xCu3O7� thin films with doping changed by field effect. The data cover the whole superconducting to insulating transition and show remarkable similarities with the effect of chemical doping in high critical temperature superconductors. The results suggest that the add-on of carriers is accompanied by an electronic phase separation, independent on the details of the doping mechanism.

The room temperature out-of-plane magnetization of epitaxial thin films of La0.67Sr0.33MnO3 on SrTiO3 (001) has been investigated with magnetic force microscopy, using magnetic tips with very small coercivity, relative to the film. A clear magnetic pattern in the form of a checkerboard, with domain dimensions of a few hundred nanometers, was found for the thin, coherently strained films, which is approximately aligned along the maximum strain [110] and [1[overline 1]0] directions in the film. With increasing in-plane applied magnetic field, the magnetic contrast reduces, reflecting the rotation of the magnetization vector into the plane of the film. This process is reversible with the field. The out-of-plane magnetic pattern is not sensitive to rotation of the in-plane field. We attribute the observed out-of-plane magnetization component to an out-of-plane magnetic anisotropy, which is a remainder of the [111] magnetic easy axis in bulk La0.67Sr0.33MnO3 single crystal.

The mechanism of field-effect doping in the 123 high critical temperature superconductors (HTS) has been investigated by x-ray absorption spectroscopy in the presence of an electric field. We demonstrate that holes are created at the CuO chains of the charge reservoir and that field-effect doping of the CuO 2 planes occurs by charge transfer, from the chains to the planes, of a fraction of the overall induced holes. The electronic properties of the charge reservoir and of the dielectric-HTS interface determine the electric field doping of the CuO 2 planes.

We demonstrate a giant polarization splitting of the emission of a high quality monolithic microcavity with an embedded ultrathin organic tetrakis(4-methoxyphenyl)porphyrin layer. The usual employed mechanism, based on the mismatch between the center of the mirror stopband and the wavelength of the microcavity, accounts only for a small fraction of the observed splitting. Optical and atomic force microscopy measurements allowed us to attribute it to local crystalline molecular order. This opens the way for the design and optimization of highly polarized compact optical sources.

The mechanism of field-effect doping in the 123 high critical temperature superconductors (HTS) has been investigated by x-ray absorption spectroscopy in the presence of an electric field. We demonstrate that holes are created at the CuO chains of the charge reservoir and that field-effect doping of the CuO(2) planes occurs by charge transfer, from the chains to the planes, of a fraction of the overall induced holes. The electronic properties of the charge reservoir and of the dielectric-HTS interface determine the electric field doping of the CuO(2) planes.

Polarized x-ray absorption spectroscopy (XAS) at the copper ${L}_{2,3}$ and oxygen $K$ edges has been used to study the superconducting-insulating (S-I) transition in ${\mathrm{Nd}}_{1.2}{\mathrm{Ba}}_{1.8}{\mathrm{Cu}}_{3}{\mathrm{O}}_{7+x}$ epitaxial films, realized by reducing the thickness from $9\phantom{\rule{0.3em}{0ex}}\text{to}\phantom{\rule{0.3em}{0ex}}6\phantom{\rule{0.3em}{0ex}}\text{unit}\phantom{\rule{0.3em}{0ex}}\text{cells}$. XAS shows that the main differences between the superconducting and the insulating films cannot be ascribed to changes of Cu density of states within the conducting $\mathrm{Cu}{\mathrm{O}}_{2}$ planes, but rather to the increase of the $3{d}_{3{z}^{2}\ensuremath{-}{r}^{2}}$ states of copper and to the effective reduction of the charge transfer of holes to the oxygen $2{p}_{xy}$ orbitals in the $\mathrm{Cu}{\mathrm{O}}_{2}$ planes. The experimental results show that the S-I transition is related to the hole localization at the Cu sites of the charge reservoir layer, i.e., outside the $\mathrm{Cu}{\mathrm{O}}_{2}$ planes, while the electronic states, lying within the conducting planes, appear to be similar in the insulating and superconducting states.

The structure of SrTiO3 (100) (STO) single crystal surfaces has been investigated by grazing incidence x-ray diffraction. The authors found that chemically etched STO is composed similar to 75% of an ideal TiO2 surface layer and similar to 25% of SrO and it is very stable when annealed in ultrahigh vacuum or in O-2 at high temperatures. A monolayer of SrO, epitaxially grown by pulsed laser deposition, is found to cover only a fraction of the TiO2 layers and exhibits a 2x2 reconstruction with strong structural changes after annealing in conditions typically used for the deposition of oxides. (c) 2007 American Institute of Physics.