Anomalous density of states in a metallic film in proximity with a superconductor

We investigated the local electronic density of states in superconductor-normal metal (Nb-Au) bilayers using a very low temperature (60 mK) STM. High resolution tunneling spectra measured on the normal metal (Au) surface show a clear proximity effect with an energy gap of reduced amplitude compared to the bulk superconductor (Nb) gap. Within this mini-gap, the density of states does not reach zero and shows clear sub-gap features. We show that the experimental spectra cannot be described with the well-established Usadel equations from the quasi-classical theory.Comment: 4 pages, 5 figure

Local spectroscopy of a proximity superconductor at very low temperature

We performed the local spectroscopy of a Normal-metal--Superconductor (N-S) junction with the help of a very low temperature (60 mK) Scanning Tunneling Microscope (STM). The spatial dependence of the local density of states was probed locally in the vicinity of the N-S interface. We observed spectra with a fully-developed gap in the regions where a thin normal metal layer caps the superconductor dot. Close to the S metal edge, a clear pseudo-gap shows up, which is characteristic of the superconducting proximity effect in the case of a long normal metal. The experimental results are compared to the predictions of the quasiclassical theory.Comment: 7 pages, 3 figure

A very low temperature STM for the local spectroscopy of mesoscopic structures

We present the design and operation of a very-low temperature Scanning Tunneling Microscope (STM) working at $60 mK$ in a dilution refrigerator. The STM features both atomic resolution and micron-sized scanning range at low temperature. This work is the first experimental realization of a local spectroscopy of mesoscopic structures at very low temperature. We present high-resolution current-voltage characteristics of tunnel contacts and the deduced local density of states of hybrid Superconductor-Normal metal systems.Comment: 5 pages, 5 figures, slightly corrected versio

Room temperature spin filtering in epitaxial cobalt-ferrite tunnel barriers

We report direct experimental evidence of room temperature spin filtering in magnetic tunnel junctions (MTJs) containing CoFe2O4 tunnel barriers via tunneling magnetoresistance (TMR) measurements. Pt(111)/CoFe2O4(111)/gamma-Al2O3(111)/Co(0001) fully epitaxial MTJs were grown in order to obtain a high quality system, capable of functioning at room temperature. Spin polarized transport measurements reveal significant TMR values of -18% at 2 K and -3% at 290 K. In addition, the TMR ratio follows a unique bias voltage dependence that has been theoretically predicted to be the signature of spin filtering in MTJs containing magnetic barriers. CoFe2O4 tunnel barriers therefore provide a model system to investigate spin filtering in a wide range of temperatures.Comment: 6 pages, 3 figure

Entre Pauline Kergomard et Maria Montessori

Au XIXe siècle les références concernant l’éducation de la petite enfance ont pris deux orientations différentes. L’une donne comme modèle la mère éducatrice. Dans l’autre référence,  l’éducatrice très respectueuse de la dynamique de l’enfant, intervient le moins possible. Deux femmes pédagogues sont représentatives de ces courants : D’une part, Pauline Kergomard (inspectrice des écoles maternelles, 1838-1925) auteur de « L’éducation maternelle à l’école » présente comme référence « la mère intelligente et dévouée » ;  elle représente plutôt la dimension « soin ». D’autre part, Maria Montessori (pédagogue italienne,1870-1952) auteur de « La pédagogie scientifique » va peu à peu imposer ses idées basées sur le fait que l’enfant possède les qualités nécessaires pour grandir par lui-même. Nous la considérons comme représentant le concept d’éducation fruit d’une méthode.  Notre propos est de nous servir de l’analyse de ces deux orientations pour dévoiler combien les soins  sont indispensables à la qualité de l’éducation même.Care and Education. Between Pauline Kergomard and María Montessori. In the 19th century the references concerning the education in the early years of infants took 2 different orientations. One uses an “educational mother” as the model. Between the love and limits that she offers her child, she brings a moral education. In the other reference, the educator, very respectful to the dynamic of the child, intervenes as little as possible. The objective is that he conquers autonomy and learns a sense of responsibilities. Two educated women are representative of these 2 tendencies: On one hand Pauline Kergomard (preschool inspector 1838 – 1925), author of “the motherly education at school”, in her teaching to school principals, presents as a reference the “comprehensive and devoted mother” taking care of the physical intellectual and moral development of children. In this case she represents more the  dimension of “care”. (keywords : knowledge, respect, tenderness, harmony, sensitivity, dignity). On the other hand, Maria Montessori, (Italian pedagogue, 1870-1952) author of scientific education”, is going to imput little by little her ideas based on the fact that the child has the necessary qualities to grow on his/her own. So according to the educator with just creating a high-quality environment in order to enable the child to find the extract to grow up and be the autor of their own evolution. We consider her to represent the concept of education, resulting from a method. (Keywords and key concepts: science, leave from, confidence, respect for the child and autonomy). We have presented the essence of both authors convictions. Alter restoring them in their context, we will confront them to see in what degree these methods are opposed or not, in the sense of seeing how they complete and intervene with each other. Our idea is to make use of  the analysis of  both orientations and develop to what point care is indispensable to the quality and the education of child and more over at the present time

Le regard des médecins topographes sur l’Algérie coloniale

Dans la continuité d’un champ d’investigation sociologique et historique qui interroge le rôle de la science occidentale dans la colonisation, cet article vise à prolonger et approfondir le débat sur la place spécifique qu’y occupe la médecine. À travers l’étude d’une source, les topographies médicales, et dans un contexte historique et géographique précis, l’Algérie de la conquête (1830-1871), l’auteur souhaite montrer en quoi le médecin participe pleinement à l’effort colonial, non pas tant en s’appropriant les corps qu’en apportant une contribution décisive à l’appropriation de l’espace lui-même.In the continuity of a sociological and historical research field which addresses the role of western science in colonization, this article extends the debate on the particular place of medicine. Through the study of a specific source, medical topographies, and within a precise historical and geographic context, the conquest of Algeria (1830-1871), the author demonstrates that physicians fully participate in the colonial effort, not so much through the appropriation of bodies, but more specifically through their decisive contribution to the appropriation of space itself.Este artículo se inscribe en la continuidad de un campo de investigación sociológica e histórica que cuestiona el papel de la ciencia en la colonización occidental y trata de ampliar el debate y de profundizar los conocimientos sobre el lugar específico que ocupa la medicina. A través del estudio de una fuente, las topografías médicas, y en un contexto histórico y geográfico específico de la conquista de Argelia (1830-1871), el autor quiere mostrar cómo el médico participa plenamente en el esfuerzo colonial, no tanto por la apropiación de los cuerpos sino más también a realizar un aporte decisivo a la apropiación del espacio por sí mismo

Band unfolding with a general transformation matrix: from code implementation to interpretation of photoemission spectra

Unfolding of a supercell band structure into a primitive Brillouin zone is important for understanding implications of structural distortions, disorder, defects, solid solutions on materials electronic structure. Necessity of the band unfolding is also recognised in interpretation of angle-resolved photoemission spectroscopy (ARPES) measurements. We describe an extension of the fold2Bloch package by implementing an arbitrary transformation matrix used to establish a relation between primitive cell and supercell. This development allows us to overcome limitations of supercells constructed exclusively by scaling of primitive cell lattice vectors. It becomes possible to transform between primitive and conventional cells as well as include rotations. The fold2Bloch is publicaly available from a GitHub repository as a FORTRAN code. It interfaces with the all-electron full-potential WIEN2k and the pseudopotential VASP density functional theory packages. The fold2Bloch is supplemented by additional pre- and post-processing utilities that aid in generating k points in the supercell (such that they later fall onto a desired path in the primitive Brillouin zone after unfolding) and plotting the unfolded band structure. We selected Sr$_2$IrO$_4$ as an illustrative example and, for the first time, present its properly unfolded band structure in direct comparison with ARPES measurements. In addition, critical importance of the band unfolding for interpretation of SrIrO$_3$ ARPES data is illustrated and discussed as a perspective.Comment: 30 pages, 7 figures, 2 tables, supporting information is not include

Nano-yarn carbon nanotube fiber based enzymatic glucose biosensor

This is the author's accepted manuscript. The final published article is available from the link below. Copyright @ 2010 IOP Publishing Ltd.A novel brush-like electrode based on carbon nanotube (CNT) nano-yarn fiber has been designed for electrochemical biosensor applications and its efficacy as an enzymatic glucose biosensor demonstrated. The CNT nano-yarn fiber was spun directly from a chemical-vapor-deposition (CVD) gas flow reaction using a mixture of ethanol and acetone as the carbon source and an iron nano-catalyst. The fiber, 28 µm in diameter, was made of bundles of double walled CNTs (DWNTs) concentrically compacted into multiple layers forming a nano-porous network structure. Cyclic voltammetry study revealed a superior electrocatalytic activity for CNT fiber compared to the traditional Pt–Ir coil electrode. The electrode end tip of the CNT fiber was freeze-fractured to obtain a unique brush-like nano-structure resembling a scale-down electrical 'flex', where glucose oxidase (GOx) enzyme was immobilized using glutaraldehyde crosslinking in the presence of bovine serum albumin (BSA). An outer epoxy-polyurethane (EPU) layer was used as semi-permeable membrane. The sensor function was tested against a standard reference electrode. The sensitivities, linear detection range and linearity for detecting glucose for the miniature CNT fiber electrode were better than that reported for a Pt–Ir coil electrode. Thermal annealing of the CNT fiber at 250 °C for 30 min prior to fabrication of the sensor resulted in a 7.5 fold increase in glucose sensitivity. The as-spun CNT fiber based glucose biosensor was shown to be stable for up to 70 days. In addition, gold coating of the electrode connecting end of the CNT fiber resulted in extending the glucose detection limit to 25 µM. To conclude, superior efficiency of CNT fiber for glucose biosensing was demonstrated compared to a traditional Pt–Ir sensor.Brunel University, the Royal Society and the National Institute of Health