Superconductivity and Dirac Fermions in 112-phase Pnictides

This article reviews the status of current research on the 112-phase of pnictides. The 112-phase has gained augmented attention due to the recent discovery of high-temperature superconductivity in \cl with a maximum critical temperature \tc\sim 47\,K upon Sb substitution. The structural, magnetic, and electronic properties of \cl bear some similarities with other superconducting pnictide phases, however, the different valence states of the pnictogen and the presence of a metallic spacer layer are unique features of the 112-system. Low-temperature superconductivity which coexists with antiferromagnetic order was observed in transition metal (Ni, Pd) deficient 112-compounds like \cn, \lpb, \lps, \lns. Besides superconductivity, the presence of naturally occurring anisotropic Dirac Fermionic states were observed in the layered 112-compounds \smb, \cmb, \lab which are of significant interest for future nanoelectronics as an alternative to graphene. In these compounds, the linear energy dispersion resulted in a high magnetoresistance that stayed unsaturated even at the highest applied magnetic fields. Here, we describe various 112-type materials systems combining experimental results and theoretical predictions to stimulate further research on this less well-known member of the pnictide family.Comment: 18 pages, 20 figure

Large Deployable Reflector (LDR) feasibility study update

In 1982 a workshop was held to refine the science rationale for large deployable reflectors (LDR) and develop technology requirements that support the science rationale. At the end of the workshop, a set of LDR consensus systems requirements was established. The subject study was undertaken to update the initial LDR study using the new systems requirements. The study included mirror materials selection and configuration, thermal analysis, structural concept definition and analysis, dynamic control analysis and recommendations for further study. The primary emphasis was on the dynamic controls requirements and the sophistication of the controls system needed to meet LDR performance goals

Learned Indexes with Updates

The present research intends to analyze the performance of Learned Indexes, having as starting point the internship held at SAP SE in Walldorf, Germany, between April,2022 and September,2022. While recent research on Learned Indexes within Database Manage ment Systems has demonstrated significant performance improvements over traditional indexes such as B-trees, there is still much to be explored in this area. Currently, there is a lack of studies on dynamic data, particularly those involving real-world datasets. Given the potential for significant gains in performance when implemented in Database Man agement Systems as compared to traditional indexes, there is a great deal of interest in conducting a comprehensive study of Learned Indexes. So the objective of this project is to benchmark several cases, initially artificially created one so we can explore some deep learning model difficulties and analyse how the database behaves. In the initial phase of this project, we established a baseline by reproducing results from previous research. We observed that our results closely resembled the behavior reported in those papers. How ever, when working with artificially created datasets, we noticed some overfitting in the model and its impact on the model’s creation and insertion.A presente pesquisa pretende analisar o comportamento de Learned Indexes, tendo como ponto de partida o estágio realizado na SAP SE em Walldorf, Alemanha, no período de abril de 2022 a setembro de 2022. Pesquisas recentes sobre Learned Indexes em Sistema de Gerenciamento de Banco de Dados tem demonstrado melhorias significativas de desempenho em relação a índices tradicionais, como B-trees, porém ainda há muito a ser explorado nessa área. Atualmente, há uma carência de estudos sobre dados dinâmicos, principalmente aqueles envolvendo conjuntos de dados reais. Dado o potencial de ganhos significativos de desempenho quando implementados em Sistema de Gerenciamento de Banco de Dados em comparação com os índices tradicionais, há um grande interesse em conduzir um estudo mais aprofundado de Learned Indexes. Assim, o objetivo deste projeto é fazer benchmark de três casos, inicialmente criados artificialmente para que possamos explorar algumas dificuldades do modelo de aprendizado profundo e analisar como o banco de dados se comporta. Na fase inicial deste projeto, estabelecemos uma linha de base reproduzindo resultados de pesquisas anteriores. Observamos que nossos resultados se assemelham bastante ao comportamento relatado nesses artigos. No entanto, ao tra balhar com conjuntos de dados criados artificialmente, notamos overfitting nos modelos utilizados e seu impacto na criação e inserção do model

Resonant transport through midgap states in voltage-biased Josephson junctions of d-wave superconductors

We study theoretically the ac Josephson effect in voltage biased planar junctions of d-wave superconductors. For some orientations of the superconductors a current peak is found at finite voltage in the current-voltage characteristics. We pick out the relevant physical processes and write down an analytical formula for the current which clearly shows how the midgap state acts as a resonance and produces the peak. We present a possible explanation for the zero-bias conductance peak, recently found in experiments on grain boundary junctions of high-temperature superconductors, in terms of resonant transmission through midgap state of quasiparticles undergoing multiple Andreev reflections. We note that within our framework the zero-bias conductance peak appears in rather transparent Josephson junctions of d-wave superconductors.Comment: 10 pages, 5 figures, Submitted to a special volume of "Superlattices and Microstructures

Charge Transport and Quantum Phase Transitions in Singlet Superconductor - Ferromagnet - Singlet Superconductor Junctions

We study the Josephson current, I_J, in a junction consisting of two s-wave superconductors that are separated by a ferromagnetic barrier possessing a magnetic and non-magnetic scattering potential, g and Z, respectively. We discuss the general dependence of I_J on g, Z, and the phase difference \phi between the two superconductors. Moreover, we compute the critical current, I_c for given g and Z, and show that it possesses two lines of non-analyticity in the (g, Z)-plane. We identify those regions in the (g, Z)-plane where the Josephson current changes sign with increasing temperature without a change in the relative phase between the two superconductors, i.e., without a transition between a 0 and \pi state of the junction. Finally, we show that by changing the relative phase \phi, it is possible to tune the junction through a first-order quantum phase transition in which the spin polarization of the two superconductors' combined ground state changes from =0 to =1/2.Comment: final version, published in Phys. Rev.

Large two-level magnetoresistance effect in doped manganite grain boundary junctions

We performed a systematic analysis of the tunneling magnetoresistance (TMR) effect in single grain boundary junctions formed in epitaxial La(2/3)Ca(1/3)MnO(3) films deposited on SrTiO(3) bicrystals. For magnetic fields H applied parallel to the grain boundary barrier, an ideal two-level resistance switching behavior with sharp transitions is observed with a TMR effect of up to 300% at 4.2 K and still above 100% at 77 K. Varying the angle between H and the grain boundary results in differently shaped resistance vs H curves. The observed behavior is explained within a model of magnetic domain pinning at the grain boundary interface.Comment: 4 pages, 3 figures, to appear in Phys. Rev. B (Rapid Comm.

Magnetic field dependence of the penetration depth of d-wave superconductors with strong isolated impurities

A d-wave superconductor with isolated strong non-magnetic impurities should exhibit an upturn in the penetration depth at low temperatures. Here we calculate how an external magnetic field supresses this effect.Comment: 2 pages, 1 figure, to appear in Physica C (proceedings for the M2S-RIO Conference, May 25-30, Rio de Janeiro, Brazil

Structure of the Ag(110) surface determined by using averaged leed intensities

The constant momentum transfer averaging method has been used to determine the surface structure of the Ag(110) surface. A contraction of 8% of the first layer spacing compared to the bulk value is found by comparing the shape of the averaged intensity profiles with kinematic calculations rather than the position of the peaks. This result agrees well with that obtained by a multiple scattering calculation