Effects of the electrostatic environment on superlattice Majorana nanowires

Finding ways of creating, measuring, and manipulating Majorana bound states (MBSs) in superconducting-semiconducting nanowires is a highly pursued goal in condensed matter physics. It was recently proposed that a periodic covering of the semiconducting nanowire with superconductor fingers would allow both gating and tuning the system into a topological phase while leaving room for a local detection of the MBS wave function. We perform a detailed, self-consistent numerical study of a three-dimensional (3D) model for a finite-length nanowire with a superconductor superlattice including the effect of the surrounding electrostatic environment, and taking into account the surface charge created at the semiconductor surface. We consider different experimental scenarios where the superlattice is on top or at the bottom of the nanowire with respect to a back gate. The analysis of the 3D electrostatic profile, the charge density, the low-energy spectrum, and the formation of MBSs reveals a rich phenomenology that depends on the nanowire parameters as well as on the superlattice dimensions and the external back-gate potential. The 3D environment turns out to be essential to correctly capture and understand the phase diagram of the system and the parameter regions where topological superconductivity is establishedWe thank E. J. H. Lee, H. Beidenkopf, E. G. Michel, N. Avraham, H. Shtrikman, and J. Nygård for valuable discussions. Research supported by the Spanish MINECO through Grants No. FIS2016-80434-P, No. BES-2017-080374, and No. FIS2017-84860-R (AEI/FEDER, EU), the European Union's Horizon 2020 research and innovation programme under the FETOPEN Grant Agreement No. 828948 and Grant Agreement LEGOTOP No. 788715, the Ramón y Cajal programme RYC-2011-09345, the María de Maeztu Programme for Units of Excellence in R&D (MDM-2014-0377), the DFG (CRC/Transregio 183, EI 519/7- 1), the Israel Science Foundation (ISF), and the Binational Science Foundation (BSF

Elaboración de diapositivas

Presenta formación para la elaboración del material de proyección fija necesario para la ilustración o desarrollo de un tema específico.Presents training for the preparation of the fixed projection material necessary for the illustration or development of a specific theme.Objetivo -- Autoprueba de avance -- Introducción -- Transparencias de 35 mm: tamaño área de foto o proyección, marcos de cartón, placas de vidrio -- Transparencias manuales en acetato: elaboración de transparencias con tinta·china -- Elaboración de diapositivas con letra-set: proceso -- Requisitos metodológicos -- Recapitulación -- Auto-evaluacion final.na33 página

Zero-energy pinning from interactions in Majorana nanowires

Majorana zero modes at the boundaries of topological superconductors are charge-neutral, an equal superposition of electrons and holes. This ideal situation is, however, hard to achieve in physical implementations, such as proximitized semiconducting nanowires of realistic length. In such systems Majorana overlaps are unavoidable and lead to their hybridization into charged Bogoliubov quasiparticles of finite energy, which, unlike true zero modes, are affected by electronic interactions. We here demonstrate that these interactions, particularly with bound charges in the dielectric surroundings, drastically change the non-interacting paradigm. Remarkably, interactions may completely suppress Majorana hybridization around parity crossings, where the total charge in the nanowire changes. This effect, dubbed zero-energy pinning, stabilizes Majoranas back to zero energy and charge, and leads to electronically incompressible parameter regions wherein Majoranas remain insensitive to local perturbations, despite their overlapWe thank K. Flensberg for illuminating discussions. We acknowledge financial support from the Spanish Ministry of Economy and Competitiveness through the Ramón y Cajal program RYC-2013-14645 and RYC-2011-09345, grant Nos. FIS2012-33521, FIS2013-47328-C2-1-P, FIS2014-55486-P, FIS2015-65706-P, FIS2015-64654-P (MINECO/FEDER), and the “María de Maeztu” Program for Units of Excellence in R&D (MDM-2014-0377

Interaction-induced zero-energy pinning and quantum dot formation in Majorana nanowires

Majorana modes emerge in non-trivial topological phases at the edges of specific materials such as proximitized semiconducting nanowires under an external magnetic field. Ideally, they are non-local states that are charge-neutral superpositions of electrons and holes. However, in nanowires of realistic length their wave functions overlap and acquire a finite charge that makes them susceptible to interactions, specifically with the image charges that arise in the electrostatic environment. Considering a realistic threedimensional model of the dielectric surroundings, here we show that, under certain circumstances, these interactions lead to a suppression of the Majorana oscillations predicted by simpler theoretical models, and to the formation of low-energy quantum-dot states that interact with the Majorana modes. Both features are observed in recent experiments on the detection of Majoranas and could thus help to properly characterize themResearch supported by the Spanish Ministry of Economy and Competitiveness through Grants FIS2014-55486-P, FIS2016-80434-P (AEI/FEDER, EU), the Ramón y Cajal programme Grants RYC-2011-09345 and the María de Maeztu Programme for Units of Excellence in R&D (MDM-2014-0377

Improved effective equation for the Rashba spin-orbit coupling in semiconductor nanowires

Semiconductor Rashba nanowires are quasi-one dimensional systems that have large spin-orbit (SO) coupling arising from a broken inversion symmetry due to an external electric field. There exist parametrized multiband models that can describe accurately this effect. However, simplified single band models are highly desirable to study geometries of recent experimental interest, since they may allow to incorporate the effects of the low dimensionality and the nanowire electrostatic environment at a reduced computational cost. Commonly used conduction band approximations, valid for bulk materials, greatly underestimate the SO coupling in Zinc-blende crystal structures and overestimate it for Wurtzite ones when applied to finite cross-section wires, where confinement effects turn out to play an important role. We demonstrate here that an effective equation for the linear Rashba SO coupling of the semiconductor conduction band can reproduce the behavior of more sophisticated eight-band k$\cdot$p model calculations. This is achieved by adjusting a single effective parameter that depends on the nanowire crystal structure and its chemical composition. We further compare our results to the Rashba coupling extracted from magnetoconductance measurements in several experiments on InAs and InSb nanowires, finding excellent agreement. This approach may be relevant in systems where Rashba coupling is known to play a major role, such as in spintronic devices or Majorana nanowires.Comment: 26 pages, 9 figures. v3: final version with new figures and new discussion of confinement effect

Tunable proximity effects and topological superconductivity in ferromagnetic hybrid nanowires

Hybrid semiconducting nanowire devices combining epitaxial superconductor and ferromagnetic insulator layers have been recently explored experimentally as an alternative platform for topological superconductivity at zero applied magnetic field. In this proof-of-principle work we show that the topological regime can be reached in actual devices depending on some geometrical constraints. To this end, we perform numerical simulations of InAs wires in which we explicitly include the superconducting Al and magnetic EuS shells, as well as the interaction with the electrostatic environment at a self-consistent mean-field level. Our calculations show that both the magnetic and the superconducting proximity effects on the nanowire can be tuned by nearby gates thanks to their ability to move the wavefunction across the wire section. We find that the topological phase is achieved in significant portions of the phase diagram only in configurations where the Al and EuS layers overlap on some wire facet, due to the rather local direct induced spin polarization and the appearance of an extra indirect exchange field through the superconductor. While of obvious relevance for the explanation of recent experiments, tunable proximity effects are of interest in the broader field of superconducting spintronics.Comment: 16 pages, 11 figures. v2: final versio

A Multisensory Analysis of the Moisture Course of the Cave of Altamira (Spain): Implications for Its Conservation

[EN] This paper addresses the conservation problems of the cave of Altamira, a UNESCO World Heritage Site in Santillana del Mar, Cantabria, Spain, due to the effects of moisture and water inside the cave. The study focuses on the description of methods for estimating the trajectory and zones of humidity from the external environment to its eventual dripping on valuable cave paintings. To achieve this objective, several multisensor remote sensing techniques, both aerial and terrestrial, such as 3D laser scanning, a 2D ground penetrating radar, photogrammetry with unmanned aerial vehicles, and high-resolution terrestrial techniques are employed. These tools allow a detailed spatial analysis of the moisture and water in the cave. The paper highlights the importance of the dolomitic layer in the cave and how it influences the preservation of the ceiling, which varies according to its position, whether it is sealed with calcium carbonate, actively dripping, or not dripping. In addition, the crucial role of the central fracture and the areas of direct water infiltration in this process is examined. This research aids in understanding and conserving the site. It offers a novel approach to water-induced deterioration in rock art for professionals and researchers.This research was funded by the Department of Innovation, Industry, Tourism and Trade of the Regional Government of Cantabria in the context of aid to encourage industrial research and innovation in companies, project "SImulador Climático del Karst de cuevas de especial valor. (SICLIKA)", grant number 2016/INN/25.Bayarri, V.; Prada, A.; García García, F.; De Las Heras, C.; Fatás, P. (2024). A Multisensory Analysis of the Moisture Course of the Cave of Altamira (Spain): Implications for Its Conservation. Remote Sensing. 16(1). https://doi.org/10.3390/rs1601019716

Fluxoid-induced pairing suppression and near-zero modes in quantum dots coupled to full-shell nanowires

We analyze the subgap excitations and phase diagram of a quantum dot (QD) coupled to a semiconducting nanowire fully wrapped by a superconducting (S) shell. We take into account how a Little-Parks (LP) pairing fluxoid (a winding in the S phase around the shell) influences the proximity effect on the dot. We find that under axially symmetric QD-S coupling, shell fluxoids cause the induced pairing to vanish, producing instead a level renormalization that pushes subgap levels closer to zero energy and flattens fermionic parity crossings as the coupling strength increases. This fluxoid-induced stabilization mechanism has analoges in symmetric S-QD-S Josephson junctions at phase π, and can naturally lead to patterns of near-zero modes weakly dispersing with parameters in all but the zeroth lobe of the LP spectru

Fluxoid-induced pairing suppression and near-zero modes in quantum dots coupled to full-shell nanowires

We analyze the subgap excitations and phase diagram of a quantum dot (QD) coupled to a semiconducting nanowire fully wrapped by a superconducting (S) shell. We take into account how a Little-Parks (LP) pairing fluxoid (a winding in the S phase around the shell) influences the proximity effect on the dot. We find that under axially symmetric QD-S coupling, shell fluxoids cause the induced pairing to vanish, producing instead a level renormalization that pushes subgap levels closer to zero energy and flattens fermionic parity crossings as the coupling strength increases. This fluxoid-induced stabilization mechanism has analoges in symmetric S-QD-S Josephson junctions at phase π, and can naturally lead to patterns of near-zero modes weakly dispersing with parameters in all but the zeroth lobe of the LP spectru

Desarrollar políticas de seguridad en teléfonos inteligentes con sistema operativo Android utilizados en la Policía Nacional

El presente proyecto está dirigido a identificar las vulnerabilidades presentadas para el uso de teléfonos inteligentes con sistema operativo Android en la Policía Nacional, con el fin de minimizar el riesgo al cual está expuesta la información de la institución, mediante la definición de nuevas políticas de seguridad de la información, dando aplicabilidad a la norma ISO/IEC 27001:2013. Se tiene como objetivo general identificar y definir políticas de seguridad de la información en dispositivos móviles con sistema Operativo Android para los funcionarios de la Policía Nacional. El presente proyecto está fundamentado metodológicamente en el carácter propositivo, en la etapa inicial se realizó un análisis de las aplicaciones más utilizadas por los funcionarios de la Policía Nacional, con el fin de identificar las tendencias en el uso de las mismas. En la segunda fase se realizó un análisis por medio de prácticas de penetración, ingeniería social, ataques y análisis de tráfico en smartphone con sistema operativo Android utilizados en la Policía Nacional, aplicando los objetivos y criterios de un Hacking Ético. Finalmente, en la tercera fase se desarrolló la definición de Políticas de Seguridad, teniendo en cuenta las vulnerabilidades encontradas y la interpretación de la información recolectada mediante un análisis cualitativo y cuantitativo, buscando a si crear conciencia en cada uno del personal que conforma la Policía Nacional, que la utilización de dispositivos móviles con sistema operativo Android debe ser de forma segura y responsable cuando se maneja información personal y/o corporativaThis project aims to identify vulnerabilities presented for the use of smart phones with Android operating system in the National Police, in order to minimize the risk to which information is displayed institution, by defining new security policies information, giving applicability to the ISO / IEC 27001: 2013. General objective is to identify and define security policies of information on mobile devices with Android operating system for officials of the National Police. This project is methodologically based on the proactive nature, in the initial stage an analysis of the most used applications by officials of the National Police, in order to identify trends in the use of them was performed. In the second phase analysis practices through penetration, social engineering attacks and traffic analysis smartphone with Android operating system at the National Police, applying the objectives and criteria of Ethical Hacking it was performed. Finally, in the third phase defining Security Policy it was developed, taking into account the vulnerabilities found and interpretation of the information collected through a qualitative and quantitative analysis, looking at whether to create awareness in each staff that makes up the National Police that the use of mobile devices with Android operating system must be safe and responsible when personal and / or corporate is handled