Quantum chaos in nanoelectromechanical systems

We present a theoretical study of the electron-phonon coupling in suspended nanoelectromechanical systems (NEMS) and investigate the resulting quantum chaotic behavior. The phonons are associated with the vibrational modes of a suspended rectangular dielectric plate, with free or clamped boundary conditions, whereas the electrons are confined to a large quantum dot (QD) on the plate's surface. The deformation potential and piezoelectric interactions are considered. By performing standard energy-level statistics we demonstrate that the spectral fluctuations exhibit the same distributions as those of the Gaussian Orthogonal Ensemble (GOE) or the Gaussian Unitary Ensemble (GUE), therefore evidencing the emergence of quantum chaos. That is verified for a large range of material and geometry parameters. In particular, the GUE statistics occurs only in the case of a circular QD. It represents an anomalous phenomenon, previously reported for just a small number of systems, since the problem is time-reversal invariant. The obtained results are explained through a detailed analysis of the Hamiltonian matrix structure.Comment: 14 pages, two column

Anomalous quantum chaotic behavior in nanoelectromechanical structures

It is predicted that for sufficiently strong electron-phonon coupling an anomalous quantum chaotic behavior develops in certain types of suspended electro-mechanical nanostructures, here comprised by a thin cylindrical quantum dot (billiard) on a suspended rectangular dielectric plate. The deformation potential and piezoelectric interactions are considered. As a result of the electron-phonon coupling between the two systems the spectral statistics of the electro-mechanic eigenenergies exhibit an anomalous behavior. If the center of the quantum dot is located at one of the symmetry axes of the rectangular plate, the energy level distributions correspond to the Gaussian Orthogonal Ensemble (GOE), otherwise they belong to the Gaussian Unitary Ensemble (GUE), even though the system is time-reversal invariant.Comment: 4 pages, pdf forma

El aprendizaje-servicio en la universidad: pedagogía y capital social para los estudiantes

Es un hecho que, al menos en España, con la puesta en marcha del Espacio Europeo de la Educación Superior, la universidad creció en atención y sensibilidad estratégica hacia determinadas cuestiones de corte pedagógico en su articulación curricular, impulsando en los Campus planes de formación inicial y continua de su profesorad

Diseño y validación de un cuestionario sobre práctica docente y actitud del profesorado universitario hacia la innovación (CUPAIN)

Introducción: La institucionalización del Aprendizaje-Servicio (ApS) en la universidad recomienda, en primer lugar, el análisis de la cultura docente del profesorado y su actitud hacia la innovación. Precisamente, lo que este trabajo pretende es aportar un modelo teórico integrador desarrollando tres escalas de evaluación, contrastadas a través de pruebas estadísticas, para el contexto de la enseñanza universitaria en España. Metodología: A fin de elaborar el modelo de medida se aplicaron tres escalas a 1903 profesoras y profesores de 6 universidades españolas: una escala de práctica docente (18 ítems), otra sobre compromiso social de la universidad (9 ítems), y una tercera, sobre prácticas docentes innovadoras (11 ítems). Los datos obtenidos se sometieron a análisis factorial exploratorio y confirmatorio, además de realizar análisis de ítems y de consistencia interna de la escala. Resultados: La solución resultante ofreció en el caso de la práctica docente una escala final de 12 ítems, distribuidos en tres factores, con índices de ajuste satisfactorios: χ2 / gl = 8.6; GFI =.96; CFI = .93; RMSEA = .064; SRMR = .039. La segunda de las escalas, unifactorial, con los 9 ítems iniciales, cuenta con una elevada consistencia interna. Y la tercera de las escalas distribuye sus 11 ítems en dos factores que muestran índices de ajuste satisfactorios: χ2 / gl = 16.34; GFI =.93; CFI = .90; RMSEA = .090; SRMR = .049. Conclusión: Los resultados de los análisis factoriales realizados ofrecen una solución satisfactoria, tanto en la estructura factorial de las escalas como en los niveles de consistencia interna evaluados. Así, el modelo de medida propuesto integra las diversas aportaciones teóricas previas, y ofrece una escala complementaria que puede contribuir al avance de la investigación en ApS y, por extensión, en las Ciencias de la Educación

Controlling the polarization and vortex charge of attosecond high-harmonic beams via simultaneous spin–orbit momentum conservation

[EN]Optical interactions are governed by both spin and angular momentum conservation laws, which serve as a tool for controlling light–matter interactions or elucidating electron dynamics and structure of complex systems. Here, we uncover a form of simultaneous spin and orbital angular momentum conservation and show, theoretically and experimentally, that this phenomenon allows for unprecedented control over the divergence and polarization of extreme-ultraviolet vortex beams. High harmonics with spin and orbital angular momenta are produced, opening a novel regime of angular momentum conservation that allows for manipulation of the polarization of attosecond pulses—from linear to circular—and for the generation of circularly polarized vortices with tailored orbital angular momentum, including harmonic vortices with the same topological charge as the driving laser beam. Our work paves the way to ultrafast studies of chiral systems using high-harmonic beams with designer spin and orbital angular momentum.The authors are thankful for useful and productive conversations with E. Pisanty, C. Durfee, D. Hickstein, S. Alperin and M. Siemens. H.C.K. and M.M.M. graciously acknowledge support from the Department of Energy BES Award No. DE-FG02–99ER14982 for the experimental implementation, as well as a MURI grant from the Air Force Office of Scientific Research under Award No. FA9550–16–1–0121 for the theory. J.L.E., N.J.B. and Q.L.N. acknowledge support from National Science Foundation Graduate Research Fellowships (Grant No. DGE-1144083). C.H.-G., J.S.R. and L.P. acknowledge support from Junta de Castilla y León (SA046U16) and Ministerio de Economía y Competitividad (FIS2013–44174-P, FIS2016–75652-P). C.H.-G. acknowledges support from a 2017 Leonardo Grant for Researchers and Cultural Creators, BBVA Foundation. L.R. acknowledges support from Ministerio de Educación, Cultura y Deporte (FPU16/02591). A.P. acknowledges support from the Marie Sklodowska-Curie Grant, Agreement No. 702565. We thankfully acknowledge the computer resources at MareNostrum and the technical support provided by Barcelona Supercomputing Center (RES-AECT-2014–2–0085). This research made use of the high-performance computingresources of the Castilla y León Supercomputing Center (SCAYLE, www.scayle.es),financed by the European Regional Development Fund (ERDF). Certain commercial instruments are identified to specify the experimental study adequately. This does not imply endorsement by the National Institute of Standards and Technology (NIST) or that the instruments are the best available for the purpose