Quantum melting of the quasi-two-dimensional vortex lattice in kappa-(ET)2Cu(NCS)2

We report torque magnetization measurements in regions of the mixed state phase diagram (${\bf B}\sim\mu_o{\bf H}_{c2}$ and T$_c$/$10^3$) of the organic superconductor $\kappa-$(ET)$_2$Cu(NCS)$_2$ where quantum fluctuations are expected to dominate thermal effects. Over most of the field range below the irreversibility line (${\bf B}_{irr}$), magneto-thermal instabilities are observed in the form of flux jumps. The abrupt cessation of these instabilities just below ${\bf B}_{irr}$ indicates a quantum melting transition from a quasi-two-dimensional vortex lattice phase to a quantum liquid phase.Comment: 8 pages (inc. Figs), accepted for publication in Phys. Rev. Let

Remarks on the fractal dimension of bi-space global and exponential attractors

Bi-spaces global and exponential attractors for the time continuous dynamical systems are considered and the bounds on their fractal dimension are discussed in the context of the smoothing properties of the system between appropriately chosen function spaces. A unified analytic semigroup approach to abstract parabolic equations is described and applications to the sample problems are given

Instrumentation for Millimeter-wave Magnetoelectrodynamic Investigations of Low-Dimensional Conductors and Superconductors

We describe instrumentation for conducting high sensitivity millimeter-wave cavity perturbation measurements over a broad frequency range (40-200 GHz) and in the presence of strong magnetic fields (up to 33 tesla). A Millimeter-wave Vector Network Analyzer (MVNA) acts as a continuously tunable microwave source and phase sensitive detector (8-350 GHz), enabling simultaneous measurements of the complex cavity parameters (resonance frequency and Q-value) at a rapid repetition rate (approx. 10 kHz). We discuss the principal of operation of the MVNA and the construction of a probe for coupling the MVNA to various cylindrical resonator configurations which can easily be inserted into a high field magnet cryostat. We also present several experimental results which demonstrate the potential of the instrument for studies of low-dimensional conducting systems.Comment: 20 pages including fig

Evidence for Anisotropic Vortex Dynamics and Pauli Limitation in the Upper Critical Field of FeSe1-xTex

We have determined HC2(T) for FeSe1-xTex (x=0.52) single crystals using resistivity measurements at high static and pulsed magnetic field, as well as specific heat measurements up to 9T. We find that the significant anisotropy of the initial slope of HC2(T) determined from resistivity measurements, is not present when HC2 is determined from the specific heat results. This suggests that the thermodynamic upper critical field is almost isotropic, and that anisotropic vortex dynamics play a role. Further evidence of anisotropic vortex dynamics is found in the behaviour in pulsed field. We also find that Pauli limiting must be included in order to fit the temperature dependence of HC2, indicating probably higher effective mass in FeSe1-xTex than in other Fe superconductors

Fermi Surface Study of Quasi-Two-Dimensional Organic Conductors by Magnetooptical Measurements

Magnetooptical measurements of several quasi-two-dimensional (q2D) organic conductors, which have simple Fermi surface structure, have been performed by using a cavity perturbation technique. Despite of the simple Fermi surface structure, magnetooptical resonance results show a dramatic difference for each sample. Cyclotron resonances (CR) were observed for q-(BEDT-TTF)2I3 and (BEDT-TTF)3Br(pBIB), while periodic orbit resonances (POR) were observed for (BEDT-TTF)2Br(DIA) and (BEDT-TTF)3Cl(DFBIB). The selection of the resonance seems to correspond with the skin depth for each sample. The effective mass of POR seems to have a mass enhancement due to the many-body effect, while effective mass of CR is independent of the strength of the electron-electron interaction. The scattering time deduced from each resonance's linewidth will be also presented.Comment: 10 pages, 8 figures, to be published to J. Phys. Soc. Jpn Vol.72 No.1 (accepted

Iniciación al mundo profesional y la investigación en ingeniería: integración de metodologías docentes

En este trabajo se expone el desarrollo de la asignatura optativa "Energía del Hidrógeno" de la titulación de Ingeniero Naval y Oceánico (E.T.S. I. Navales UPM) que se ha venido impartiendo a alumnos de los cursos 4º y 5º indistintamente y tiene asignados 4,5 créditos de docencia. La asignatura se organiza de modo que permite acercar a los alumnos que la cursan al ejercicio de la profesión y al conocimiento de la actividad investigadora. Una parte de los temas la imparte el profesor y otra parte la preparan e imparten los alumnos formando grupos. Trabajando en equipo, los alumnos estudian y profundizan en los temas de la asignatura, algunos de los cuales diseñan, preparan, escriben y finalmente exponen, tras varias sesiones de tutoría con el profesor. Moderan un debate sobre el tema expuesto y diseñan y organizan una sesión de aprendizaje cooperativo. A lo largo del curso habitualmente manejan documentación y artículos científicos en lengua inglesa. Se graban las clases y se publican en la plataforma virtual de enseñanza y/o Youtube, se escriben artículos científicos y se siguen unas pautas establecidas para elaborar los documentos generados. Se organizan visitas externas y se realizan prácticas de laboratorio. Se sigue el método de b-learning con evaluación continua y coevaluación y se aplica a lo largo de todo el curso la metodología de Aprendizaje Cooperativo. El conjunto de actividades desarrolladas y el modo de impartir la asignatura constituye una metodología fácilmente aplicable a cursos de Máster y actualmente se está trabajando en las modificaciones requeridas para su implantación en el Máster de Ingeniería Naval y Oceánica.Los autores desean agradecer a la Universidad Politécnica de Madrid su ayuda y soporte en este trabajo, en el marco del Proyecto de Innovación Educativa IE1415-08002

Nyquist method for Wigner-Poisson quantum plasmas

By means of the Nyquist method, we investigate the linear stability of electrostatic waves in homogeneous equilibria of quantum plasmas described by the Wigner-Poisson system. We show that, unlike the classical Vlasov-Poisson system, the Wigner-Poisson case does not necessarily possess a Penrose functional determining its linear stability properties. The Nyquist method is then applied to a two-stream distribution, for which we obtain an exact, necessary and sufficient condition for linear stability, as well as to a bump-in-tail equilibrium.Comment: 6 figure

Neutron diffraction analysis of stress and strain partitioning in a two-phase microstructure with parallel-aligned phases

By time-of-flight (TOF) neutron diffraction experiments, the influence of segregation-induced microstructure bands of austenite (γ) and martensite (α′ ) phases on the partitioning of stress and strain between these phases was investigated. Initially, tensile specimens of a Co-added stainless steel were heat treated by quenching and partitioning (Q&P) processing. Tensile specimens were subsequently loaded at 350 °C parallel to the length of the bands within the apparent elastic limit of the phase mixture. Lattice parameters in both axial and transverse directions were simultaneously measured for both phases. The observation of a lattice expansion for the γ phase in the transverse direction indicated a constraint on the free transverse straining of γ arising from the banded microstructure. The lateral contraction of α′ imposed an interphase tensile microstress in the transverse direction of the γ phase. The multiaxial stress state developed in the γ phase resulted in a large deviation from the level of plastic strain expected for uniaxial loading of single phase γ. Since segregation-induced banded microstructures commonly occur in many engineering alloys, the analysis of stress and strain partitioning with the present Q&P steel can be used to interpret the observations made for further engineering alloys with two-phase microstructures