Spin decoherence of magnetic atoms on surfaces

We review the problem of spin decoherence of magnetic atoms deposited on a surface. Recent breakthroughs in scanning tunnelling microscopy (STM) make it possible to probe the spin dynamics of individual atoms, either isolated or integrated in nanoengineered spin structures. Transport pump and probe techniques with spin polarized tips permit measuring the spin relaxation time T1T1, while novel demonstration of electrically driven STM single spin resonance has provided a direct measurement of the spin coherence time T2T2 of an individual magnetic adatom. Here we address the problem of spin decoherence from the theoretical point of view. First we provide a short general overview of decoherence in open quantum systems and we discuss with some detail ambiguities that arise in the case of degenerate spectra, relevant for magnetic atoms. Second, we address the physical mechanisms that allows probing the spin coherence of magnetic atoms on surfaces. Third, we discuss the main spin decoherence mechanisms at work on a surface, most notably, Kondo interaction, but also spin–phonon coupling and dephasing by Johnson noise. Finally, we briefly discuss the implications in the broader context of quantum technologies.JFR acknowledges financial supported by MEC-Spain (FIS2013-47328-C2-2-P) and Generalitat Valenciana (ACOMP/2010/070), Prometeo. This work is funded by ERDF funds through the Portuguese Operational Program for Competitiveness and Internationalization COMPETE 2020, and National Funds through FCT – The Portuguese Foundation for Science and Technology, under the project ‘‘PTDC/FIS-N AN/4662/2014” (016656). FD acknowledges funding by the Ministerio de Economía y Competitividad (MINECO, Spain), with grant MAT2015-66888-C3-2-R., and Gobierno Vasco by grant IT986-16

Graphene single-electron transistor as a spin sensor for magnetic adsorbates

We study single-electron transport through a graphene quantum dot with magnetic adsorbates. We focus on the relation between the spin order of the adsorbates and the linear conductance of the device. The electronic structure of the graphene dot with magnetic adsorbates is modeled through numerical diagonalization of a tight-binding model with an exchange potential. We consider several mechanisms by which the adsorbate magnetic state can influence transport in a single-electron transistor: tuning the addition energy, changing the tunneling rate, and in the case of spin-polarized electrodes, through magnetoresistive effects. Whereas the first mechanism is always present, the others require that the electrode has to have either an energy- or spin-dependent density of states. We find that graphene dots are optimal systems to detect the spin state of a few magnetic centers.This work has been financially supported by MEC-Spain (Grant Nos. FIS2010-21883-C02-01 and CONSOLIDER CSD2007-0010) as well as Generalitat Valenciana, grant Prometeo 2012-11

Sedentary Time Accumulated in Bouts is Positively Associated with Disease Severity in Fibromyalgia: The Al-andalus Project

To examine the associations of prolonged sedentary time (ST) with disease severity in women with fibromyalgia, and to analyse the combined association of total ST and prolonged ST with the disease severity in this population. Women (n = 451; 51.3 +/- 7.6 years old) with fibromyalgia participated. Sedentary time and moderate-to-vigorous physical activity (MVPA) were measured using triaxial accelerometry and ST was processed into 30- and 60-min bouts. Dimensions of fibromyalgia (function, overall, symptoms) and the overall disease impact were assessed with the Revised Fibromyalgia Impact Questionnaire (FIQR). Body fat percentage was assessed using a bio-impedance analyser, and physical fitness was assessed with the Senior Fitness Tests Battery. Greater percentage of ST in 30-min bouts and 60-min bouts were associated with worse function, overall, symptoms and the overall impact of the disease (all, P 60-min bouts) presented lower overall impact compared to participants with high levels of total ST and prolonged ST (mean difference = 6.56; 95% confidence interval (CI) = 1.83 to 11.29, P = 0.002). Greater percentage of ST accumulated in 30- and 60-min bouts and a combination of high levels of total and prolonged ST are related to worse disease severity. Although unable to conclude on causality, results suggest it might be advisable to motivate women with fibromyalgia to break prolonged ST and reduce their total daily ST

RKKY oscillations in the spin relaxation rates of atomic-scale nanomagnets

Exchange interactions with itinerant electrons are known to act as a relaxation mechanism for individual local spins. The same exchange interactions induce the so-called RKKY indirect exchange interaction between two otherwise decoupled local spins. Here, we show that both the spin relaxation and the RKKY coupling can be seen as the dissipative and reactive response to the coupling of the local spins with the itinerant electrons. We thereby predict that the spin relaxation rates of magnetic nanostructures of exchanged coupled local spins, such as nanoengineered spin chains, have an oscillatory dependence on kFd, where kF is the Fermi wave number and d is the interspin distance, very much like the celebrated oscillations in the RKKY interaction. We demonstrate that both T1 and T2 can be enhanced or suppressed, compared to the single-spin limit, depending on the interplay between the Fermi surface and the nanostructure geometrical arrangement. Our results open a route to engineer spin relaxation and decoherence in atomically designed spin structures.J.F.R. acknowledges financial supported by MEC-Spain (Grant No. FIS2013-47328-C2-2-P) and Generalitat Valenciana (Grant No. ACOMP/2010/070), Prometeo. This work is funded by ERDF funds through the Portuguese Operational Program for Competitiveness and InternationalizationÐ COMPETE 2020, and National Funds through FCT-The Portuguese Foundation for Science and Technology, under the project PTDC/FIS-NAN/4662/2014 (Project.No. 016656). F.D. acknowledges support from Spanish Government through Grant No.MAT2015-66888-C3-2-R and Basque Government, Grant No. IT986-16

Enhanced lifetimes of spin chains coupled to chiral edge states

We consider spin relaxation of finite-size spin chains exchanged coupled with a one-dimensional (1D) electron gas at the edge of a quantum spin Hall (QSH) insulator. Spin lifetimes can be enhanced due to two independent mechanisms. First, the suppression of spin-flip forward scattering inherent in the spin momentum locking of the QSH edges. Second, the reduction of spin-flip backward scattering due to destructive interference of the quasiparticle exchange, modulated by k F d, where d is the inter-spin distance and k F is the Fermi wavenumber of the electron gas. We show that the spin lifetime of the S = 1/2 ground state of odd-numbered chains of antiferromagnetically coupled S = 1/2 spins can be increased more than 4 orders of magnitude by properly tuning the product k F d and the spin size N, in strong contrast with the 1D case. Possible physical realizations together with some potential issues are also discussed.JFR acknowledges financial support by FCT- The Portuguese Foundation for Science and Technology, under the project ‘PTDC/FIS-NAN/4662/2014’ (016656), MINECO-Spain (Grant No. MAT2016-78625-C2) and Generalitat Valenciana Prometeo2017/139. FD acknowledges financial support from Spanish Government through grants MAT2015-66888-C3-2-R, Basque Government, grant IT986-16 and Canary Islands program Viera y Clavijo (Ref. 2017/0000231). FD acknowledges the hospitality of the Departamento de Física Aplicada of the Universidad de Alicante

Comparison between two-fluid model simulations and particle image analysis & velocimetry (PIV) results for a two-dimensional gas-solid fluidized bed

This work compares simulation and experimental results of the hydrodynamics of a two-dimensional, bubbling air-fluidized bed. The simulation in this study has been conducted using an Eulerian–Eulerian two-fluid approach based on two different and well-known closure models for the gas–particle interaction: the drag models due to Gidaspow and Syamlal & O'Brien. The experimental results have been obtained by means of Digital Image Analysis (DIA) and Particle Image Velocimetry (PIV) techniques applied on a real bubbling fluidized bed of 0.005 m thickness to ensure its two-dimensional behaviour. Several results have been obtained in this work from both simulation and experiments and mutually compared. Previous studies in literature devoted to the comparison between two-fluid models and experiments are usually focused on bubble behaviour (i.e. bubble velocity and diameter) and dense-phase distribution. However, the present work examines and compares not only the bubble hydrodynamics and dense-phase probability within the bed, but also the time-averaged vertical and horizontal component of the dense-phase velocity, the air throughflow and the instantaneous interaction between bubbles and dense-phase. Besides, quantitative comparison of the time-averaged dense-phase probability as well as the velocity profiles at various distances from the distributor has been undertaken in this study by means of the definition of a discrepancy factor, which accounts for the quadratic difference between simulation and experiments The resulting comparison shows and acceptable resemblance between simulation and experiments for dense-phase probability, and good agreement for bubble diameter and velocity in two-dimensional beds, which is in harmony with other previous studies. However, regarding the time-averaged velocity of the dense-phase, the present study clearly reveals that simulation and experiments only agree qualitatively in the two-dimensional bed tested, the vertical component of the simulated dense-phase velocity being nearly an order of magnitude larger than the one obtained from the PIV experiments. This discrepancy increases with the height above the distributor of the two-dimensional bed, and it is even larger for the horizontal component of the time-averaged dense-phase velocity. In other words, the results presented in this work indicate that the fine agreement commonly encountered between simulated and real beds on bubble hydrodynamics is not a sufficient condition to ensure that the dense-phase velocity obtained with two-fluid models is similar to that from experimental measurements on two-dimensional bedsThis work has been partially funded by the Spanish Government (ProjectDPI2009-10518) and the Autonomous Community of Madrid (ProjectS2009/ENE-1660). Their supports are greatly appreciatedPublicad

Exposición al benceno en las estaciones de servicio

Fossil fuels have a wide range of by-product uses, the range of hydrocarbons are today one of the largest sources of energy on the planet, since their exploitation multiple and a large number of by-products derived from the distillation of this compound have been discovered, The fractionation of hydrocarbons has given by-products that are widely used in different areas of the transportation industry, such is the case of gasoline, a by-product from the distillation of crude oil, its use is basically focused on vehicles. In different parts of the world, different blends of gasoline are produced, in order to respond to the different needs of each region; however, its composition consists of different aromatic compounds, including benzene, which is addressed in a special way in this article by be one of the most harmful gasoline compounds to human health. In the same way, the multiple risks associated with the work carried out by gas station dispatchers are specified, always focused on exposure to benzene and other substances, mentioning the personal protective equipment necessary to minimize said risks.Los combustibles fósiles cuentan con una amplia gama de subproductos, los hidrocarburos son hoy en día una de las mayores fuentes de energía del planeta, desde su explotación se han descubierto múltiples usos y una gran cantidad de subproductos derivados de la destilación de este compuesto, el fraccionamiento de los hidrocarburos han dado subproductos que son ampliamente usados en diferentes áreas de la industria del transporte, tal es el caso de las gasolinas, un subproducto proveniente de la destilación del petróleo crudo, su uso básicamente está enfocado a los vehículos. En diferentes partes del mundo se producen diferentes mezclas de gasolina, con la finalidad de responder a las diferentes necesidades de cada región, sin embargo, su composición consta de diferentes compuestos aromáticos entre esos el benceno, el cual se aborda de manera especial en este artículo por ser uno de los compuestos de la gasolina más perjudiciales a la salud del ser humano. De igual manera se especifican los múltiples riesgos asociados al trabajo que desempeñan los despachadores de las gasolineras, enfocado siempre en la exposición al benceno y otras sustancias, mencionando los equipos de protección personal necesarios para minimizar dichos riesgos

Consequences of Kondo exchange on quantum spins

When individual quantum spins are placed in close proximity to conducting substrates, the localized spin is coupled to the nearby itinerant conduction electrons via Kondo exchange. In the strong coupling limit this can result in the Kondo effect — the formation of a correlated, many body singlet state — and a resulting renormalization of the density of states near the Fermi energy. However, even when Kondo screening does not occur, Kondo exchange can give rise to a wide variety of other phenomena. In addition to the well known renormalization of the g factor and the finite spin decoherence and relaxation times, Kondo exchange has recently been found to give rise to a newly discovered effect: the renormalization of the single ion magnetic anisotropy. Here we put these apparently different phenomena on equal footing by treating the effect of Kondo exchange perturbatively. In this formalism, the central quantity is ρJ, the product of the density of states at the Fermi energy ρ and the Kondo exchange constant J. We show that perturbation theory correctly describes the experimentally observed exchange induced shifts of the single spin excitation energies, demonstrating that Kondo exchange can be used to tune the effective magnetic anisotropy of a single spin.This work was supported by the Engineering and Physical Sciences Research Council UK (EP/D063604/1 and EP/H002367/1); the Leverhulme Trust (RPG-2012-754); the Ministry of Science and Education Spain (FIS2010-21883-C02-01, MAT2010-19236, CONSOLIDER CSD2007-0010 and Programa de Movilidad Postdoctoral); the European Commission FP7 Programme (PER-GA-2009-251791) and the GV grant Prometeo 2012–11

Manual de trabajo para diseñar los perfiles de cargos por competencias laborales en las Universidades

La presente investigación se realizó en la Universidad Central “Marta Abreu” de Las Villas, con el objetivo de elaborar un manual de trabajo que facilite el diseño de perfiles de cargos por competencias laborales en las diferentes unidades organizativas de dicho centro. Para el desempeño de este objetivo se elaboró un marco teórico referencial a partir del análisis de la bibliografía disponible y otras fuentes de información relacionadas con los temas objeto de estudio. Además, con los diferentes conceptos y herramientas encontradas acerca de competencias laborales, perfiles de cargo por competencias laborales, normas de escrituras de los manuales de procedimientos y la gestión de recursos humanos en las Instituciones de Educación Superior, se confeccionó una biblioteca de competencias laborales y a su vez un manual de procedimientos para cumplir con el objetivo propuesto en dicha institución. Con la elaboración del flujo de actividades se representaron los pasos a seguir en la elaboración de los perfiles de cargo por competencias laborales, a partir del análisis de las funciones descritas en los calificadores de cargos y los profesiogramas, identificando un conjunto de riesgos a los que se les propusieron las medidas para la minimización del efecto que implican no disponer de los mismos.La presente investigación se realizó en la Universidad Central “Marta Abreu” de Las Villas, con el objetivo de elaborar un manual de trabajo que facilite el diseño de perfiles de cargos por competencias laborales en las diferentes unidades organizativas de dicho centro. Para el desempeño de este objetivo se elaboró un marco teórico referencial a partir del análisis de la bibliografía disponible y otras fuentes de información relacionadas con los temas objeto de estudio. Además, con los diferentes conceptos y herramientas encontradas acerca de competencias laborales, perfiles de cargo por competencias laborales, normas de escrituras de los manuales de procedimientos y la gestión de recursos humanos en las Instituciones de Educación Superior, se confeccionó una biblioteca de competencias laborales y a su vez un manual de procedimientos para cumplir con el objetivo propuesto en dicha institución. Con la elaboración del flujo de actividades se representaron los pasos a seguir en la elaboración de los perfiles de cargo por competencias laborales, a partir del análisis de las funciones descritas en los calificadores de cargos y los profesiogramas, identificando un conjunto de riesgos a los que se les propusieron las medidas para la minimización del efecto que implican no disponer de los mismos

Spin excitations of individual magnetic dopants in an ionic thin film

Individual magnetic transition metal dopants in a solid host usually exhibit relatively small spin excitation energies of a few meV. Using scanning tunneling microscopy and inelastic electron tunneling spectroscopy (IETS) techniques, we have observed a high spin excitation energy around 36 meV for an individual Co substitutional dopant in ultrathin NaCl films. In contrast, the Cr dopant in the NaCl film shows much lower spin excitation energy around 2.5 meV. Electronic multiplet calculations combined with first-principles calculations confirm the spin excitation induced IETS, and quantitatively reveal the out-of-plane magnetic anisotropies for both Co and Cr. They also allow reproducing the experimentally observed redshift in the spin excitations of Co dimers and ascribe it to a charge and geometry redistribution.This research was supported by the National Natural Science Foundation of China (91961102, 11704057), the Shenzhen fundamental research funding (JCYJ20190806112206698), the starting funding from HIT Shenzhen (HA45001082), and the Research Foundation Flanders (G0D56.19N and G0A05.19N) and by the KU Leuven Research Council (C14/22/103). Financial support by the following Projects: RTI2018-097895-B-C41, PID2019-109539GB-C41 and PID2019-103910GB-I00, funded by MCIN/AEI/10.13039/501100011033/ and FEDER Una manera de hacer Europa, as well as GIU18/138 by Universidad del Pais Vasco UPV/EHU; IT-1246-19, IT986-16 and IT-1260-19 by Gobierno Vasco, is gratefully acknowledged