A band structure scenario for the giant spin-orbit splitting observed at the Bi/Si(111) interface

The Bi/Si(111) (sqrt{3} x sqrt{3})R30 trimer phase offers a prime example of a giant spin-orbit splitting of the electronic states at the interface with a semiconducting substrate. We have performed a detailed angle-resolved photoemission (ARPES) study to clarify the complex topology of the hybrid interface bands. The analysis of the ARPES data, guided by a model tight-binding calculation, reveals a previously unexplored mechanism at the origin of the giant spin-orbit splitting, which relies primarily on the underlying band structure. We anticipate that other similar interfaces characterized by trimer structures could also exhibit a large effect.Comment: 11 pages, 13 figure

Tunable spin-gaps in a quantum-confined geometry

We have studied the interplay of a giant spin-orbit splitting and of quantum confinement in artificial Bi-Ag-Si trilayer structures. Angle-resolved photoelectron spectroscopy (ARPES) reveals the formation of a complex spin-dependent gap structure, which can be tuned by varying the thickness of the Ag buffer layer. This provides a means to tailor the electronic structure at the Fermi energy, with potential applications for silicon-compatible spintronic devices

New Mechanism for Spin-Orbit Splitting of Conduction States in Surface Alloys

We present Angle-Resolved Photoelectron Spectroscopy (ARPES) data on spin-orbit split states in two XAg2 surface alloys grown on an Ag(111) substrate, and of the Si(111)-AgBiAg2 trilayer system. We briefly discuss the origin of the unusually large energy and momentum splitting, and the possibility of tuning by surface engineering the spin polarization at the Fermi level. [DOI: 10.1380/ejssnt.2009.264

Topografía de la densidad mineral osea: Método de estudio "in vivo" de la cabeza femoral humana mediante TAC

Presentamos un método, no descrito anteriormente, que permite obtener un mapa muy preciso de la distribución topográfica de la densidad mineral ósea relativa de cualquier parte del esqueleto, en el sujeto vivo, a partir de una imagen TAC convencional. El método se basa en la medición directa de los niveles de gris de la imagen TAC, los cuales guardan una relación de linealidad con las Unidades Honsfield, de manera que la densidad óptica de un punto concreto se correlaciona con la densidad ósea del mismo. En nuestro estudio lo hemos aplicado a la cabeza femoral humana, obteniendo la imagen topográfica tridimensional de sus densidades óseas.We describe a new method to obtain an accurate mapping of the bone mineral density which can be applied to any area of the human skeleton in a live subject using conventional CT scan imaging. The method involves direct measurement of grey colour intensity from the CT image. The colour intensity maintains a direct relationship with the Honsfield Units, therefore the optic density of a given area is related to the bone density. In our study this method has been applied to the human femoral head to obtain a three-dimensional topography of the bone density

Two Distinct Phases of Bilayer Graphene Films on Ru(0001)

By combining angle-resolved photoemission spectroscopy and scanning tunneling microscopy we reveal the structural and electronic properties of multilayer graphene on Ru(0001). We prove that large ethylene exposure allows to synthesize two distinct phases of bilayer graphene with different properties. The first phase has Bernal AB stacking with respect to the first graphene layer, displays weak vertical interaction and electron doping. The long-range ordered moir\'e pattern modulates the crystal potential and induces replicas of the Dirac cone and minigaps. The second phase has AA stacking sequence with respect to the first layer, displays weak structural and electronic modulation and p-doping. The linearly dispersing Dirac state reveals the nearly-freestanding character of this novel second layer phase

Anisotropic spin gaps in BiAg2_2-Ag/Si(111)

We present a detailed analysis of the band structure of the BiAg$_2$/Ag/Si(111) trilayer system by means of high resolution Angle Resolved Photoemission Spectroscopy (ARPES). BiAg2/Ag/Si(111) exhibits a complex spin polarized electronic structure due to giant spin-orbit interactions. We show that a complete set of constant energy ARPES maps, supplemented by a modified nearly free electron calculation, provides a unique insight into the structure of the spin polarized bands and spin gaps. We also show that the complex gap structure can be continuously tuned in energy by a controlled deposition of an alkali metal.Comment: 6 pages, 5 figure

Primordial black holes capture by stars and induced collapse to low-mass stellar black holes

Primordial black holes in the asteroid-mass window, which might constitute all the dark matter, can be captured by stars when they traverse them at low enough velocity. After being placed on a bound orbit during star formation, they can repeatedly cross the star if the orbit happens to be highly eccentric, slow down by dynamical friction and end up in the stellar core. The rate of these captures is highest in halos of high dark matter density and low velocity dispersion, when the first stars form at redshift ∼ 20. We compute this capture rate for low-metallicity stars of 0.3 to 1 M, and find that a high fraction of these stars formed in the first dwarf galaxies would capture a primordial black hole, which would then grow by accretion up to a mass that may be close to the total star mass. We show the capture rate of primordial black holes does not depend on their mass over this asteroid-mass window, and should not be much affected by external tidal perturbations. These low-mass stellar black holes could be discovered today in low-metallicity, old binary systems in the Milky Way containing a surviving low-mass mainsequence star or a white dwarf, or via gravitational waves emitted in a merger with another compact object. No mechanisms in standard stellar evolution theory are known to form black holes below the Chandrasekhar mass, so detecting a low-mass black hole would fundamentally impact our understanding of stellar evolution, dark matter and the early Universe.We would like to acknowledge helpful discussions and advice fromN. Bellomo, J. L. Bernal, A. Escrivà, C. Germani, and J. Sal-vadó. This work was supported in part by Spanish grants CEX-2019-000918-M funded by MCIN/AEI/10.13039/501100011033,AYA2015-71091-P, and PID2019-108122GB-C32.Peer ReviewedPostprint (author's final draft

Desarrollo de software de análisis y reconstrucción de sucesos en Cámaras de Proyección Temporal

En este trabajo se ha presentado el área de estudio conocido como Búsqueda de Sucesos Raros, así como un conjunto de fenómenos de interés que podrían mostrar nueva física y que se encuentran dentro de esta categoría. Se han mostrado descrito las Cámaras de Proyección Temporal así como sus posibles aplicaciones a este campo y proyectos que las emplean junto a la electrónica T2K en la Universidad de Zaragoza. Este tipo de detectores están caracterizados por poder ofrecer una buena resolución espacial y en energía de los eventos. En el marco de este trabajo se han elaborado un conjunto de herramientas de software, con la intención de resultar lo más transversal posible y poder se aplicado a los distintos experimentos que empleen cámaras TPC y electrónica T2K. Este software introduce una metodología mediante la cual pasa de la descripción de los eventos producida por la electrónica como 512 muestras temporales por canal a una representación del evento dada por un conjunto de N gaussianas. Este software se ha empleado en un conjunto de medidas elaboradas por el prototipo NEXT-MM. Los resultados han permitido mostrar el éxito de las herramientas en su aplicación a eventos casi puntuales, sin observar problemas de convergencia en los eventos de fondo con trazas largas. Mediante las medidas se ha caracterizado una mezcla de Xe-TMA, donde se obtenía por primera vez los coeficientes de difusión longitudinal y transversa. Los resultados han mostrado que la mezcla permite, con concentraciones muy pequeñas de TMA, una mejoría en la resolución espacial. Además se ha probado la capacidad del prototipo para ser empleado en la caracterización de gases

Design and accuracy analysis of multi-level state estimation based on smart metering infrastructure

While the first aim of smart meters is to provide energy readings for billing purposes, the availability of these measurements could open new opportunities for the management of future distribution grids. This paper presents a multi-level state estimator that exploits smart meter measurements for monitoring both low and medium voltage grids. The goal of the paper is to present an architecture able to efficiently integrate smart meter measurements and to show the accuracy performance achievable if the use of real-time smart meter measurements for state estimation purposes were enabled. The design of the state estimator applies the uncertainty propagation theory for the integration of the data at the different hierarchical levels. The coordination of the estimation levels is realized through a cloud-based infrastructure, which also provides the interface to auxiliary functions and the access to the estimation results for other distribution grid management applications. A mathematical analysis is performed to characterize the estimation algorithm in terms of accuracy and to show the performance achievable at the different levels of the distribution grid when using the smart meter data. Simulations are presented, which validate the analytical results and demonstrate the operation of the multi-level estimator in coordination with the cloud-based platform