Universality in the transport response of molecular wires physisorbed onto graphene electrodes

We analyze the low-voltage transport response of large molecular wires bridging graphene electrodes, where the molecules are physisorbed onto the graphene sheets by planar anchor groups. In our study, the sheets are pulled away to vary the gap length and the relative atomic positions. The molecular wires are also translated in directions parallel and perpendicular to the sheets. We show that the energy position of the Breit-Wigner molecular resonances is universal for a given molecule, in the sense that it is independent of the details of the graphene edges, gaps lengths or of the molecule positions. We discuss the need to converge carefully the k-sampling to provide reasonable values of the conductance.Comment: 6 pages, 6 figure

Symmetry-induced interference effects in metalloporphyrin wires

Organo-metallic molecular structures where a single metallic atom is embedded in the organic backbone are ideal systems to study the effect of strong correlations on their electronic structure. In this work we calculate the electronic and transport properties of a series of metalloporphyrin molecules sandwiched by gold electrodes using a combination of density functional theory and scattering theory. The impact of strong correlations at the central metallic atom is gauged by comparing our results obtained using conventional DFT and DFT+U approaches. The zero bias transport properties may or may not show spin-filtering behavior, depending on the nature of the d state closest to the Fermi energy. The type of d state depends on the metallic atom and gives rise to interference effects that produce different Fano features. The inclusion of the U term opens a gap between the d states and changes qualitatively the conductance and spin-filtering behavior in some of the molecules. We explain the origin of the quantum interference effects found as due to the symmetry-dependent coupling between the d states and other molecular orbitals and propose the use of these systems as nanoscale chemical sensors. We also demonstrate that an adequate treatment of strong correlations is really necessary to correctly describe the transport properties of metalloporphyrins and similar molecular magnets

Impact of Fano and Breit-Wigner resonances in the thermoelectric properties of nanoscale junctions

We show that the thermoelectric properties of nanoscale junctions featuring states near the Fermi level strongly depend on the type of resonance generated by such states, which can be either Fano- or Breit-Wigner-like. We give general expressions for the thermoelectric coefficients generated by the two types of resonances and calculate the thermoelectric properties of these systems, which encompass most nanoelectronics junctions. We include simulations of real junctions where metalloporphyrins dithiolate molecules bridge gold electrodes and prove that for some metallic elements the thermoelectric properties show a large variability with respect to the position of the resonance near the Fermi level. We find that the thermopower and figure of merit are largely enhanced when the resonance gets close to the Fermi level and reach values higher than typical values found in other nanoscale junctions. The specific value and temperature dependence are determined by a series of factors such as the strength of the coupling between the state and other molecular states, the symmetry of the state, the strength of the coupling between the molecule and the leads and the spin-filtering behavior of the junction. © 2013 American Physical Society.The research presented in this paper was funded by the Spanish MICINN through Grant No. FIS2012-34858 and by the Marie Curie network NanoCTM. V.M.G.S. thanks the Spanish Ministerio de Economía y Competitividad for a Ramón y Cajal fellowship (RYC-2010-06053). R.R.F. thanks Consejería de Educación del Principado de Asturias for a Severo Ochoa grant (Grant No. BP11-069).Peer Reviewe

Relaciones escuelas-familias: la laboriosa tarea de construir la cooperación

This article serves as an introduction to the monograph of this issue presenting our reflections on educational (and also political) importance of implementing measures to promote the relationship between families and schools. Departing from the Spanish reality, we offer a proposal for the classification of specific forms of parental involvement in children’s education centers. Then we analyze some conceptions that underlie these kinds of relationships that we consider deviants. In our opinion these relations are true blind alleys, that do not lead anywhere (never toward a realistic partnership). We end our reflections by mentioning some fundamental characteristics of the attitudes that allow such kind of fruitful families involvement. Finally, as coordinator of this monograhp, I will introduce each of the contributions that make part of it.En este artículo que sirve de introducción a la parte monográfica de este número presentaremos nuestras reflexiones sobre la importancia educativa (también política) de poner en marcha medidas que fomenten esta relación. Ofrecemos una propuesta de esquema de clasificación de las formas concretas de participación de los padres en los centros de educación infantil a partir de la realidad española. A continuación analizamos algunas concepciones de estas relaciones que consideramos desviadas, en realidad auténticas vías muertas, que no llevan a ninguna parte (tampoco a la participación). Finalizamos afirmando algunas características fundamentales relacionadas con las actitudes que hacen posible y fructífera esta participación y presentando las contribuciones que conforman este monográfico

Elenco y biogeografía de los ácaros acuáticos (Acari, Parasitengona, Hydrachnidia) de Sudamérica

Checklist and catalog publications demonstrate a clear connection between basic taxonomy and biodiversity issues. According to some estimates, only 10-30% of all global species have been named. As in other fields, catalogs provide an important source of information concerning species diversity in freshwater ecology. <br /><br /> South America is a continent dominated by freshwater ecosystems. The tremendous habitat diversity created by this landscape supports a high number of arthropods, including water mites, which belong to the hyperdiverse group Acari. South America has a substantial task ahead in cataloging its biodiversity.<br /><br /> Much has been published on water mites in South America. In fact, according to Besch, water mites were the most studied with the exception of Europe up until the 1960’s. Most of the collections were conducted by two acarologists (Lundblad and Karl Viets) during the 1940’s. Today, the collection, identification and description process of water mites is slower. In the 1980’s, the north-american acarologist D. R. Cook produced two lengthy papers about neotropical water mites in four regions of South America. Recently, several Argentine acarologists have published papers on water mites from diverse habitats and regions in South America.<br /><br /> The catalog presented here includes information regarding 6 superfamilies, including 23 families in 118 genera of true water mites (Hydrachnidia, Parasitengona, Acari). It also includes the references concerning the species, distribution in various regions of South America and –as far as known– habitat.<br /><br /> At present, there are 916 species from several authors cataloged in 11 countries in South America. The degree of knowledge varies greatly from country to country, with numerous entries for Brazil and none for French Guiana.<br><br>Las publicaciones de catálogos y listados de especies determinan una clara conexión entre taxonomía básica y temas relacionados con la biodiversidad. Según algunas estimaciones, solo el 10-30% del número total de especies ha sido nominado.<br /><br /> El trabajo que se presenta aquí insumió años de trabajo, en la catalogación de los verdaderos ácaros acuáticos Parasitengona de América del Sur. Se agrega además información sobre la distribución por regiones y hábitats conocidos para las especies.<br /><br /> Hasta el presente hay 6 superfamilias, 23 familias, 118 géneros y 916 especies catalogados en 11 países de América del Sur. El grado de conocimiento varía enormemente de país a país con numerosos datos de Brasil y ninguno de Guayana Francesa

Anchoring and functionality profiling in single-molecule electronic junctions

Resumen del trabajo presentado a la XXXV Reunión Bienal de la Real Sociedad Española de Física y al 25º Encuentro Ibérico de Enseñanza de la Física, celebrados en Gijón (España) del 13 al 17 de julio de 2015.Single-molecule electronics has been around for a few years since its initial proposal by Aviram and Rattner in the early 70’. Its deployment as the ultimate nanoelectronics technology has been hindered by a serious lack of reproducibility and of stability, inherent to its single-particle nature. These obstacles have been tackled by the community in the past decade and are slowly being overcome. We present here our recent efforts directed to improve reproducibility and stability issues, as well as functionality.Peer Reviewe