Person: Díaz Fernández, Álvaro
Loading...
First Name
Álvaro
Last Name
Díaz Fernández
Affiliation
Universidad Complutense de Madrid
Faculty / Institute
Ciencias Físicas
Department
Física de Materiales
Area
Identifiers
7 results
Search Results
Now showing 1 - 7 of 7
Item Tailoring topological states of core-shell nanoparticles(Physica E: Low-dimensional Systems and Nanostructures, 2022) Martínez Strasser, Carolina; Baba, Yuriko; Díaz Fernández, Álvaro; Domínguez-Adame Acosta, FranciscoIn this work we investigate novel spherical core-shell nanoparticles with band inversion. The core and the embedding medium are normal semiconductors while the shell material is assumed to be a topological insulator. The envelope functions are found to satisfy a Dirac-like equation that can be solved in a closed form. The core-shell nanoparticle supports midgap bound states located at both interfaces due to band inversion. These states are robust since they are topologically protected. The energy spectrum presents mirror symmetry due to the chiral symmetry of the Dirac-like Hamiltonian. As a major result, we show that the thickness of the shell acts as an additional parameter for the fine tuning of the energy levels, which paves the way for electronics and optoelectronics applications.Item Manipulation of Majorana bound states in proximity to a quantum ring with Rashba coupling(Scientific reports, 2022) Medina, Fabián Gonzalo; Martínez, Dunkan; Díaz Fernández, Álvaro; Domínguez-Adame Acosta, Francisco; Rosales, Luis; Orellana, Pedro A.The quest for Majorana zero modes in the laboratory is an active field of research in condensed matter physics. In this regard, there have been many theoretical proposals; however, their experimental detection remains elusive. In this article, we present a realistic setting by considering a quantum ring with Rashba spin-orbit coupling and threaded by a magnetic flux, in contact with a topological superconducting nanowire. We focus on spin-polarized persistent currents to assess the existence of Majorana zero modes. We find that the Rashba spin-orbit coupling allows for tuning the position of the zero energy crossings in the flux parameter space and has sizable effects on spin-polarized persistent currents. We believe that our results will contribute towards probing the existence of Majorana zero modes.Item Electron scattering by magnetic impurity in Weyl semimetals(New journal of physics, 2021) Díaz Fernández, Álvaro; Domínguez-Adame Acosta, Francisco; Abril, Óscar deWeyl semimetals are prominent examples of topologically protected quantum matter. These materials are the three-dimensional counterparts of graphene and great efforts are being devoted to achieve a thorough understanding of their fundamental physics. In this work, we aim at contributing to this end by discussing the effect of a single magnetic impurity in Weyl semimetals as a first step towards considering a larger number of point-like impurities. We find that resonances appear in the local density of states (LDOS) with a Friedel-like behaviour, oscillating as a function of distance. By studying the spin-resolved LDOS, we can observe non-trivial and anisotropic spin textures where the spin components perpendicular to the spin of the impurity wind around the latter, until the spin becomes completely parallel to the impurity right at the impurity's location. Friedel oscillations also play a relevant role in the form of the spin textures, forming an oscillatory pattern. We believe our results can pave the way to further studies which consider the presence of a large number of random magnetic impurities.- Project number: 293
Item Actualización de material docente basado en Jupyter Notebook para su uso dentro del Plan de Internacionalización(2018) Díaz García, Elena; Cabrera Granado, Eduardo; Domínguez-Adame Acosta, Francisco; Gómez Calderón, Óscar; Melle Hernández, Sonia; Díaz Fernández, Álvaro; Villas Pazos, AlbertoLa iniciativa de este proyecto viene justificada a la vista del gran interés generado por algunos de los materiales docentes diseñados por nuestro grupo en anteriores proyectos, en los que se vienen desarrollando diferentes herramientas docentes basadas en el uso de Jupyter Notebooks. A la vista del impacto generado, y teniendo en cuenta que la evolución del proyecto Jupyter, así como las aplicaciones de distintas herramientas asociadas a Jupyter Notebook, es continua, nos planteamos como objetivo principal del presente proyecto la actualización y la puesta a disposición en inglés de nuestra producción de los últimos años. Item Robust midgap states in band-inverted junctions under electric and magnetic fields(Beilstein journal of nanotechnology, 2018) Díaz Fernández, Álvaro; del Valle, Natalia; Domínguez-Adame Acosta, FranciscoSeveral IV-VI semiconductor compounds made of heavy atoms, such as Pb1-xSnxTc, may undergo band-inversion at the L point of the Brillouin zone upon variation of their chemical composition. This inversion gives rise to topologically distinct phases, characterized by a change in a topological invariant. In the framework of the k.p theory, band-inversion can be viewed as a change of sign of the fundamental gap. A two-band model within the envelope-function approximation predicts the appearance of midgap interface states with Dirac cone dispersions in band-inverted junctions, namely, when the gap changes sign along the growth direction. We present a thorough study of these interface electron states in the presence of crossed electric and magnetic fields, the electric field being applied along the growth direction of a band-inverted junction. We show that the Dirac cone is robust and persists even if the fields are strong. In addition, we point out that Landau levels of electron states lying in the semiconductor bands can be tailored by the electric field. Tunable devices are thus likely to be realizable, exploiting the properties studied herein.- Project number: 140
Item Propuesta de una nueva metodología para la enseñanza de la física de la materia condensada: clase semipresencial con formato de taller(2022) Domínguez-Adame Acosta, Francisco; Díaz García, Elena; Chico Gómez, Leonor; Relaño Pérez, Armando; Díaz Fernández, Álvaro; Molina Fernández, Rafael Alejandro; Baba, Yuriko Caterina; López Corps, ÁngelEn este Proyecto INNOVA-Docencia hemos pretendido superar estas limitaciones académicas de las asignaturas tradicionales de grado y máster. Para ello, se ha llevado a cabo la implementación, el desarrollo y el análisis de resultados de la clase semipresencial con formato de taller, particularizada a la docencia de la FMC. Partimos del convencimiento de que este estudio es necesario incluso en el futuro, cuando la crisis sanitaria se haya superado. La UCM está haciendo ya un esfuerzo considerable para ofrecer cursos virtuales o que requieran poca presencialidad. Item Floquet engineering of Dirac cones on the surface of a topological insulator(Physical review B, 2019) Díaz Fernández, Álvaro; Díaz García, Elena; Gómez León, Álvaro; Platero, G.; Domínguez-Adame Acosta, FranciscoWe propose to Floquet engineer Dirac cones at the surface of a three-dimensional topological insulator. We show that a large tunability of the Fermi velocity can be achieved as a function of the polarization, direction, and amplitude of the driving field. Using this external control, the Dirac cones in the quasienergy spectrum may become elliptic or massive, in accordance with experimental evidence. These results help us to understand the interplay of surface states and external ac driving fields in topological insulators. In our work we use the full Hamiltonian for the three-dimensional system instead of effective surface Hamiltonians, which are usually considered in the literature. Our findings show that the Dirac cones in the quasienergy spectrum remain robust even in the presence of bulk states, and therefore, they validate the usage of effective surface Hamiltonians to explore the properties of Floquet-driven topological boundaries. Furthermore, our model allows us to introduce out-of-plane field configurations which cannot be accounted for by effective surface Hamiltonians.