"Experimental study of iron-based superconductors: advanced characterization and fundamental properties"

Iron-based superconductors (SCs) were discovered in 2008 and their specific features immediately captured the great interest of the scientific community. The critical temperature of these compounds was the highest known so far with the exception of cuprates. They show a layered crystal structure and quasi-2D Fermi surface, made up of multiple disconnected sheets, and usually with multiple order parameters. Their parent (undoped) compounds are metals and the proximity to magnetism, clearly visible in the phase diagram of these materials, seems to be of fundamental importance in order to understand the superconductivity in Fe-based SCs. Their observed features have led theoretical physicist to propose an unconventional, spin fluctuation-mediated pairing. Many experimental results obtained so far seem to confirm the theoretical predictions, but the final validation of this model still requires additional steps. The research on Fe-based materials has been recently boosted by the progress in the techniques of film deposition. Films of very high quality are necessary for applications in superconducting electronics, i.e. for the fabrication of Josephson junctions, SQUIDs and so on. However, they can be fruitfully used also to investigate fundamental properties of these compounds (especially for those materials that cannot be grown easily in the form of single crystals). For instance, they are the perfect playground for transport, optical and spectroscopic measurements of various kind; thin films offer an additional way to tune the critical temperature, thanks to strain/stress effects that can be induced by the substrate; finally, they are necessary to realize some proposed phase-sensitive experiments to determine the order parameter symmetry s++ or s± [1]. Many other experimental measurements and theoretical calculations are crucial in order to clarify some open points for example the superconducting order parameter and its symmetry, the amplitude and the number of the energy gaps and their temperature dependence. This dissertation presents the advanced characterization and the fundamental study of Fe-based superconductors (122 and 11 families) mainly in the form of epitaxial thin films by means of different experimental techniques, namely electrical transport measurements, point-contact Andreev-reflection spectroscopy (used both for advanced characterization and fundamental investigation) and other techniques for the morphological and chemical characterization of the surface (AFM, FESEM, Energy-dispersive X-ray spectroscopy). This research was developed within the activities of the Eu-Japan project IRON SEA (establishing the basic science and technology for Iron-based superconducting electronics applications) funded within the Seventh Framework Programme FP7 under grant number 283141. The epitaxial thin films of 122 and 11 superconductors were grown by partners of the consortium that are world leaders in this field, and thus they are high-quality state-ofthe- art samples. In particular, the Co-doped Ba-122 films were deposited by the group of prof. B. Holzapfel at IFW Dresden, while the Fe(Te,Se) films were grown by the group of prof. A. Maeda at Tokyo University. The data collected by means of the aforementioned techniques allowed the systematic characterization and the study of the homogeneity of the superconducting properties and of the chemical composition at the surface, and also the effects of aging and degradation (especially for Ba-122 samples). In the framework of the IRON SEA project, this large amount of information was required in order to assess the possible use of these films for the development of superconducting electronic devices. From the point of view of the fundamental properties, the PCARS study of the Co-doped Ba-122 and Fe(Te,Se) thin films allowed gathering information about the phase diagram of these materials, i.e. the effect of isovalent and aliovalent doping on the critical temperature (Tc) and on the superconducting gaps (i.e. number, amplitude and symmetry) – or, conversely, the determination of the trend of the gaps as a function of doping and critical temperature. Thanks to a theoretical analysis of the results carried out by Dr. G. Ummarino within the multi-band Eliashberg theory, the results of PCARS measurements allowed extracting the characteristic energy of the mediating boson, verifying the spin-fluctuation mechanism, determining the evolution of the coupling constants from the underdoped to the overdoped regime. The activity of the candidate has been focused on the experimental aspects of the research. She spent two months (October - December 2012) at IFW Dresden during which she carried out a part of the PCARS measurements on Co-doped Ba-122 films (otherwise carried out at Politecnico di Torino) and contributed to their characterization (i.e. by DC Resistivity, RHEED and X-ray Spectroscopy) as discussed in chapter 4. The characterization of these films was completed at Politecnico of Torino by AFM, FESEM and EDX measurements, performed by F. Laviano and M. Raimondi and later analysed by the candidate. Similarly for Fe(Te,Se) films, widely characterized by the Japanese partner, the research was mainly focused on PCARS and transport measurements (chapter 5 )

Doping and critical-temperature dependence of the energy gaps in Ba(Fe_{1-x}Co_x)_2As_2 thin films

The dependence of the superconducting gaps in epitaxial Ba(Fe_{1-x}Co_{x})_2As_2 thin films on the nominal doping x (0.04 \leq x \leq 0.15) was studied by means of point-contact Andreev-reflection spectroscopy. The normalized conductance curves were well fitted by using the 2D Blonder-Tinkham-Klapwijk model with two nodeless, isotropic gaps -- although the possible presence of gap anisotropies cannot be completely excluded. The amplitudes of the two gaps \Delta_{S} and \Delta_{L} show similar monotonic trends as a function of the local critical temperature T_{c}^{A} (measured in the same point contacts) from 25 K down to 8 K. The dependence of the gaps on x is well correlated to the trend of the critical temperature, i.e. to the shape of the superconducting region in the phase diagram. When analyzed within a simple three-band Eliashberg model, this trend turns out to be compatible with a mechanism of superconducting coupling mediated by spin fluctuations, whose characteristic energy scales with T_{c} according to the empirical law \Omega_{0}= 4.65*k_{B}*T_{c}, and with a total electron-boson coupling strength \lambda_{tot}= 2.22 for x \leq 0.10 (i.e. up to optimal doping) that slightly decreases to \lambda_{tot}= 1.82 in the overdoped samples (x = 0.15).Comment: 8 pages, 5 color figure

Resistivity in Co-doped Ba-122: comparison of thin films and single crystals

The temperature dependence of the resistivity of epitaxial Ba(Fe_(1-x)Co_x)2As2 thin films (with nominal doping x = 0.08, 0.10 and 0.15) has been analyzed and compared with analogous measurements on single crystals taken from literature. The rho(T) of thin films looks different from that of single crystals, even when the cobalt content is the same. All rho(T) curves can be fitted by considering an effective two-band model (with holes and electrons bands) in which the electrons are more strongly coupled with the bosons (spin fluctuations) than holes, while the effect of impurities is mainly concentrated in the hole band. Within this model the mediating boson has the same characteristic energy in single crystals and thin films, but the shape of the transport spectral function at low energy has to be very different, leading to a "hardening" of the electron-boson spectral function in thin films, associated with the strain induced by the substrate.Comment: 13 pages, 4 figure

Reescritura en pareja : una tarea de aprendizaje inicial de lo escrito

This paper presents a re-writing task to be carried out in pairs by 5 to 7-year old early readers and writers. The paper aims to (i) show the importance of the pedagogical decisions undertaken by a teacher who choose to implement tasks which allow her to observe learning processes that remain hidden under other circumstances; and (ii)underscore the advanced capacities that the learners may show in their conversations and in their shared product texts when they are given the opportunity to do so. The paper concludes with a set of implications for classroom practice.En aquest article es presenta una tasca de reescriptura de textos en parella de dos infants en els moments inicials del procés d'aprenentatge del llenguatge escrit (entre 5 i 7 anys). Els objectius d'aquest article són els següents: (i) mostrar la importància de la decisió pedagògica del docent sobre el tipus de tasca que permet observar els processos d'aprenentatge que romandrien ocults en altres situacions; i (ii) cridar l'atenció sobre les capacitats que els aprenents poden arribar a mostrar tant en les interaccions verbals entre ells com en la producció de textos reescrits compartits, quan se'ls dona l'oportunitat de fer-ho. Finalment, es discuteixen els beneficis que l'aplicació a l'aula d'aquesta mena de tasca pot tenir en l'alfabetització inicial.En este artículo se presenta una tarea de reescritura de textos en pareja de dos niños en los momentos iniciales del proceso de aprendizaje del lenguaje escrito (entre 5 y 7 años). Los objetivos de este artículo son los siguientes: (i) mostrar la importancia de las decisiones pedagógicas tomadas por el docentesobre un tipo de tarea que permite observar los procesos de aprendizaje que permanecerían ocultos en otras situaciones; y (ii) llamar la atención sobre las capacidadesque los aprendices pueden llegar a mostrar tanto en las interacciones verbales entre ellos como en la producción de textos reescritos compartidos, cuando se les da la oportunidad de hacerlo. Por último, se resumen los beneficios que la utilización de este tipo de tareas puede tener en la alfabetización inicial

Rol de variantes genéticas en el desarrollo de Enfermedad Renal Crónica en pacientes con Diabetes Mellitus Tipo 2

La Enfermedad Renal Crónica (ERC) es una afección que perjudica a un gran número de pacientes. Una de las causas es la Nefropatía en pacientes con Diabetes Mellitus Tipo 2 (DM2).Objetivo: Indagar si la presencia de variantes genéticas contribuyen al desarrollo de ERC en pacientes con DM2.Materiales y métodos: se evaluaron criterios clínicos, bioquímicos y moleculares en 25 pacientes con DM2. Los polimorfismos se analizaron mediante PCR-RFLP para ECA (rs4646994); CDKAL1 (rs7756992); e-NOS (rs1799983) y SLC12A3 (rs11643718).Resultados: El análisis estadístico mediante modelo dominante arrojaron para: ECA (rs4646994) (OR=1,33 (IC 95%) 0,25-7,01; p=0,73); CDKAL1 (rs7756992) (OR= 1 (IC 95%) 0,14-7,39; p=NA); e-NOS (rs1799983) (OR= 0,29 (IC 95%) 0,05-1,57; p=0,14) y SLC12A3 (rs11643718 (OR= 1,62 (IC 95%) 0,19-13,93; p=0,66).Conclusiones: ninguna de las variantes evaluadas en los genes ECA, CDKAL1, e-NOS y SLC12A3 mostraron asociaciones positivas o negativas con el riesgo a desarrollar ERC en pacientes con DM2.Fil: Yang, Pablo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba; Argentina. Area de Ciencias Agrarias, Ingeniería, Ciencias Biológicas y de la Salud de la Universidad Católica de Córdoba; ArgentinaFil: Ojeda, Verónica. Universidad Nacional de Córdoba. Facultad de Medicina. Hospital Nacional de Clínicas; ArgentinaFil: Ruiz Pecchio, Adriana. Universidad Nacional de Córdoba. Facultad de Medicina. Hospital Nacional de Clínicas; ArgentinaFil: Soria, Néstor Walter. Area de Ciencias Agrarias, Ingeniería, Ciencias Biológicas y de la Salud de la Universidad Católica de Córdoba; Argentin

Mucormycosis - Dual Therapy with Prolonged Survival

Mucorales fungal infection is a fungal disease with potentially fatal outcomes. The most frequent involvement in humans comes from the orders known as Mucorales and Entomophthorales. Mucorales is more acute and has a predilection for immunocompromised patients. Mucorales are associated with an affinity for vessels, which leads to invasion and infarction of tissue. Mucormycosis is a devastating complication that can be a life threatening fungal invasion in many patients in an immunocompromised state