Interface superconductivity: History, developments and prospects

The concept of interface superconductivity was introduced over 50 years ago. Some of the greatest physicists of that time wondered whether a quasi-two-dimensional (2D) superconductor can actually exist, what are the peculiarities of 2D superconductivity, and how does the reduced dimensionality affect the critical temperature (Tc). The discovery of high-temperature superconductors, which are composed of coupled 2D superconducting layers, further increased the interest in reduced dimensionality structures. In parallel, the advances in experimental techniques made it possible to grow epitaxial 2D structures with atomically flat surfaces and interfaces, enabling some of the experiments that were proposed decades ago to be performed finally. Now we know that interface superconductivity can occur at the junction of two different materials (metals, insulators, semiconductors). This phenomenon is being explored intensely; it is also exploited as a means to increase Tc or to study quantum critical phenomena. This research may or may not produce a superconductor with a higher Tc or a useful superconducting electronic device but it will likely bring in new insights into the physics underlying high-temperature superconductivity

Epitaxial growth of high quality WO3 thin films

We have grown epitaxial WO3 films on various single-crystal substrates using radio frequency magnetron sputtering. While pronounced surface roughness is observed in films grown on LaSrAlO4 substrates, films grown on Y AlO3 substrates show atomically flat surfaces, as demonstrated by atomic force microscopy and X-ray diffraction (XRD) measurements. The crystalline structure has been confirmed to be monoclinic by symmetric and skew-symmetric XRD. The dependence of the growth modes and the surface morphology on the lattice mismatch are discussed

Estudio de la no participación en el programa de prevención de cáncer de mama en la ciudad de Valencia

ResumenObjetivoConocer los motivos de no participación de las mujeres en el Programa poblacional de Prevención de Cáncer de Mama.MétodosEs un estudio observacional transversal, en mujeres que fueron invitadas para participar en el Programa de Prevención de Cáncer de Mama en la ciudad de Valencia y no acudieron. Se realizó una entrevista con cuestionario en el domicilio con 25 preguntas, agrupadas en: conocimiento sobre el programa, motivos de la no participación, actitudes o creencias y características de las encuestadas (variables socioeconómicas, culturales y edad). Se analizaron las diferencias en las características de las mujeres con un análisis bivariante y multivariante mediante regresión logística.ResultadosSe utilizaron 783 direcciones, se obtuvieron 411 cuestionarios, y analizaron 361, y se excluyeron del análisis los 50 cuestionarios utilizados en la prueba piloto, ya que ésta produjo una modificación del cuestionario. El 93,4% (intervalo de confianza [IC] del 95%: 3-95,7) recordaba haber recibido una citación. El motivo principal de no participación fue estar estudiada por otros servicios sanitarios en el 48,8% (IC del 95%: 43,6-53,9), seguido de diversos motivos personales en el 16,1% (IC del 95%: 12,3-19,9) y del horario de citación que no les resultó adecuado en el 15,5% (IC del 95%:11,8-19,2). Analizando la clase social media y alta frente a la clase baja, se observan importantes diferencias: las mujeres de clase media o alta tenían mayor probabilidad de conocer el programa y llevar tratamiento hormonal sustitutivo (THS) y el motivo principal de no asistencia era el estar estudiada por otros servicios sanitarios y para las mujeres de la clase baja el temor, no considerarlo importante para su salud y problemas de accesibilidad horaria. En el análisis multivariante las variables que entraron en el modelo fueron: THS, la clase social y el nivel cultural; de tal forma que aquellas mujeres de clase social media o alta, que llevan THS y de nivel cultural medio o alto tienen mayor probabilidad de estar estudiadas.ConclusionesEl perfil de las mujeres que no participan, pertenece, por un lado, a la clase social media o alta, que toman THS y que están siendo revisadas por otros servicios sanitarios, y por otro, a un grupo de mujeres con nivel socioeconómico bajo y cuyo motivo de no participación es por temor o dificultades de horario.AbstractAimTo determine the reasons for non-participation of women in a breast cancer screening program.MethodsWe performed an observational, cross-sectional study in women who were invited to participate in the breast cancer screening program in the city of Valencia and who failed to attend. The women were interviewed in their homes through a questionnaire consisting of 25 questions grouped as follows: knowledge of the program, reasons for nonparcitipation, attitudes or beliefs and characteristics of the interviewees (socioeconomic and educational variables and age). A descriptive analysis was performed. Differences in the characteristics of women were evaluated thorugh bivariate analysis. Multivariate analysis was performed through logistic regression.ResultsA total of 783 addreses were used, 411 questionnaires were completed and 361 were analyzed. The 50 questionnaires used in the pilot study were excluded because, as a consequence of this study, the questionnaire had been modified. Most of the women (93,4%) (CI: 90.3-95.7) remembered having an appointment. The main reason for not attending was being screened in another health service in 48.8% (CI: 43.6-53.9), followed by various personal reasons in 16.1% (CI: 12.3-19.9) and inability to keep the appointment at the specified time in 15.5% (CI: 11.8-19.2). Comparison of women in the middle and upper social classes with those in the lower classes revealed important differences. Middle and upper class women had a higher probability of knowing about the program and of being on hormone replacement therapy (HRT) and the most frequent reason for non-attendance was attendance at another program run by another health service. In lower class women the reasons for non-attendance were fear, not believing the program to be important to health and inability to keep the appointment at the specified time. In the multivariate analysis, the variables that entered the model were HRT, social class and education. Thus, middle or upper class women undergoing HRT and with secondary or higher education had a higher probability of being screened.ConclusionsThe profile of non-participating women belongs on the one hand to those in the middle or upper social classes, undergoing HRT and being screened by other health services and, on the other, to a group of women of low social class, whose reason for non-participation is fear and timetable difficulties

All-thermal switching of amorphous Gd-Fe alloys: analysis of structural properties and magnetization dynamics

In recent years, there has been an intense interest in understanding the microscopic mechanism of thermally induced magnetization switching driven by a femtosecond laser pulse. Most of the effort has been dedicated to periodic crystalline structures while the amorphous counterparts have been less studied. By using a multiscale approach, i.e. first-principles density functional theory combined with atomistic spin dynamics, we report here on the very intricate structural and magnetic nature of amorphous Gd-Fe alloys for a wide range of Gd and Fe atomic concentrations at the nanoscale level. Both structural and dynamical properties of Gd-Fe alloys reported in this work are in good agreement with previous experiments. We calculated the dynamic behavior of homogeneous and inhomogeneous amorphous Gd-Fe alloys and their response under the influence of a femtosecond laser pulse. In the homogeneous sample, the Fe sublattice switches its magnetization before the Gd one. However, the temporal sequence of the switching of the two sublattices is reversed in the inhomogeneous sample. We propose a possible explanation based on a mechanism driven by a combination of the Dzyaloshiskii-Moriya interaction and exchange frustration, modeled by an antiferromagnetic second-neighbour exchange interaction between Gd atoms in the Gd-rich region. We also report on the influence of laser fluence and damping effects in the all-thermal switching.Comment: Accepted in Physical Review B as a regular article. It contains 14 pages and 14 figure

Spin excitations in a single La2_2CuO4_4 layer

The dynamics of S=1/2 quantum spins on a 2D square lattice lie at the heart of the mystery of the cuprates \cite{Hayden2004,Vignolle2007,Li2010,LeTacon2011,Coldea2001,Headings2010,Braicovich2010}. In bulk cuprates such as \LCO{}, the presence of a weak interlayer coupling stabilizes 3D N\'{e}el order up to high temperatures. In a truly 2D system however, thermal spin fluctuations melt long range order at any finite temperature \cite{Mermin1966}. Further, quantum spin fluctuations transfer magnetic spectral weight out of a well-defined magnon excitation into a magnetic continuum, the nature of which remains controversial \cite{Sandvik2001,Ho2001,Christensen2007,Headings2010}. Here, we measure the spin response of \emph{isolated one-unit-cell thick layers} of \LCO{}. We show that coherent magnons persist even in a single layer of \LCO{} despite the loss of magnetic order, with no evidence for resonating valence bond (RVB)-like spin correlations \cite{Anderson1987,Hsu1990,Christensen2007}. Thus these excitations are well described by linear spin wave theory (LSWT). We also observe a high-energy magnetic continuum in the isotropic magnetic response. This high-energy continuum is not well described by 2 magnon LSWT, or indeed any existing theories.Comment: Revised version to appear in Nature Materials; 6 pages,4 figure

Interface superconductivity: History, developments and prospects

The concept of interface superconductivity was introduced over 50 years ago. Some of the greatest physicists of that time wondered whether a quasi-two-dimensional (2D) superconductor can actually exist, what are the peculiarities of 2D superconductivity, and how does the reduced dimensionality affect the critical temperature (Tc). The discovery of high-temperature superconductors, which are composed of coupled 2D superconducting layers, further increased the interest in reduced dimensionality structures. In parallel, the advances in experimental techniques made it possible to grow epitaxial 2D structures with atomically flat surfaces and interfaces, enabling some of the experiments that were proposed decades ago to be performed finally. Now we know that interface superconductivity can occur at the junction of two different materials (metals, insulators, semiconductors). This phenomenon is being explored intensely; it is also exploited as a means to increase Tc or to study quantum critical phenomena. This research may or may not produce a superconductor with a higher Tc or a useful superconducting electronic device but it will likely bring in new insights into the physics underlying high-temperature superconductivity

Heat-conserving three-temperature model for ultrafast demagnetization of 3d ferromagnets

We study the ultrafast magnetization dynamics of bcc Fe and fcc Co using the recently suggested heat-conserving three-temperature model (HC3TM), together with atomistic spin- and lattice dynamics simulations. It is shown that this type of Langevin-based simulation is able to reproduce observed trends of the ultrafast magnetization dynamics of fcc Co and bcc Fe, in agreement with previous findings for fcc Ni. The simulations are performed by using parameters that to as large extent as possible are obtained from electronic structure theory. The one parameter that was not calculated in this way, was the damping term used for the lattice dynamics simulations, and here a range of parameters were investigated. It is found that this term has a large influence on the details of the magnetization dynamics. The dynamics of iron and cobalt is compared with previous results for nickel and similarities and differences in the materials' behavior are analysed following the absorption of a femtosecond laser pulse. Importantly, for all elements investigated so far with this model, we obtain a linear relationship between the value of the maximally demagnetized state and the fluence of the laser pulse, which is in agreement with experiments.Comment: 9 pages, 9 figures, Submitted to Physical Review

Influence of non-local damping on magnon properties of ferromagnets

We study the influence of non-local damping on magnon properties of Fe, Co, Ni and Fe$_{1-x}$Co$_{x}$ ($x=30\%,50\%$) alloys. The Gilbert damping parameter is typically considered as a local scalar both in experiment and in theoretical modelling. However, recent works have revealed that Gilbert damping is a non-local quantity that allows for energy dissipation between atomic sites. With the Gilbert damping parameters calculated from a state-of-the-art real-space electronic structure method, magnon lifetimes are evaluated from spin dynamics and linear response, where a good agreement is found between these two methods. It is found that non-local damping affects the magnon lifetimes in different ways depending on the system. Specifically, we find that in Fe, Co, and Ni the non-local damping decreases the magnon lifetimes, while in $\rm Fe_{70}Co_{30}$ and Fe$_{50}$Co$_{50}$ an opposite, non-local damping effect is observed, and our data show that it is much stronger in the former