Electrostatic interface tuning in correlated superconducting heterostructures

An electrostatic field, which is applied to a gated high-temperature superconducting (HTSC) film, is believed to affect the film similar to charge doping. Analyzing the pairing in terms of a t-J model, we show that a coupling to electric dipoles and phonons at the interface of film and dielectric gate localizes the injected charge and leads to a superconductor-insulator transition. This results in a dramatic modification of the doping dependent phase diagram close to and above the optimal doping which is expected to shed light on recent electric field-effect experiments with HTSC cuprates.Comment: 6 pages, 6 figures, to appear in Physical Review

Emerging magnetism and electronic phase separation at titanate interfaces

The emergence of magnetism in otherwise nonmagnetic compounds and its underlying mechanisms have become the subject of intense research. Here we demonstrate that the nonmagnetic oxygen vacancies are responsible for an unconventional magnetic state common for titanate interfaces and surfaces. Using an effective multiorbital modelling, we find that the presence of localized vacancies leads to an interplay of ferromagnetic order in the itinerant t2g band and complex magnetic oscillations in the orbitally-reconstructed eg-band, which can be tuned by gate fields at oxide interfaces. The magnetic phase diagram includes highly fragmented regions of stable and phase-separated magnetic states forming beyond nonzero critical defect concentrations.Comment: 5 pages, 4 figure

Magnetically ordered state at correlated oxide interfaces: the role of random oxygen defects

Using an effective one-band Hubbard model with disorder, we consider magnetic states of the correlated oxide interfaces, where effective hole self-doping and a magnetially ordered state emerge due to electronic and ionic reconstructions. By employing the coherent potential approximation, we analyze the effect of random oxygen vacancies on the two-dimensional magnetism. We find that the random vacancies enhance the ferromagnetically ordered state and stabilize a robust magnetization above a critical vacancy concentration of about c=0.1. In the strong-correlated regime, we also obtain a nonmonotonic increase of the magnetization upon an increase of vacancy concentration and a substantial increase of the magnetic moments, which can be realized at oxygen reduced high-Tc cuprate interfaces.Comment: 8 pages, 2 figures, submitted to J Supercond Novel Magnetism (ICSM12 conference contribution

Interstitial Fe-Cr alloys: Tuning of magnetism by nanoscale structural control and by implantation of nonmagnetic atoms

Using the density functional theory, we perform a full atomic relaxation of the bulk ferrite with 12.5%-concentration of monoatomic interstitial Cr periodically located at the edges of the bcc Fe$_\alpha$ cell. We show that structural relaxation in such artificially engineered alloys leads to significant atomic displacements and results in the formation of novel highly stable configurations with parallel chains of octahedrically arranged Fe. The enhanced magnetic polarization in the low-symmetry metallic state of this type of alloys can be externally controlled by additional inclusion of nonmagnetic impurities like nitrogen. We discuss possible applications of generated interstitial alloys in spintronic devices and propose to consider them as a basis of novel durable types of stainless steels.Comment: 8 pages, 10 figure

Mechanism of orbital reconstruction at the interfaces of transition metal oxides

Orbital reconstruction at interfaces between YBa2Cu3O6 and SrO-terminated SrTiO3 is studied using local spin density approximation (LSDA) with intra-atomic Coulomb repulsion (LSDA+U). The change of population of interfacial Cu 3d orbitals results in stabilization of a new oxidation state $3d^8$ which involves an additional modification of orbital occupancies in the nearest SrO and TiO2 layers. We find that an increase of electron charge in Cu 3d_{x^2-y^2} states counterbalances a depopulation of 3d_{3z^2-r^2} orbitals which induces, on account of the onsite Coulomb repulsion U, a splitting of 3d_{3z^2-r^2} states at CuO2-SrO interfaces.Comment: 7 pages, 7 figures, to appear in Physical Review

Cogito, ergo sum : del entimema a la bioética

The work analyzes the Cartesian expression “cogito ergosum” from the points of view of the traditional and the modern logics. The expression is shown to be an enthymeme with the major premise omitted. Two ways of the major premise interpretation are made clear: 1) as a conventional assertion (a most commonly accepted view among philosophers); 2) as a proposition containing an equivalence. It is shown that the equivalence of “thinking and being” assumed by Descartes has once opened up the logical-anthropological opportunity to proclaim as “non-existing” what does not think. The last assertion provides the basis of “Ratiofundamentalism”. The work demonstrates that the Cartesian enthymeme analysis concerns directly our understanding of the ontological status of man and is inseparable from the questions of biomedical ethics.El trabajo analiza la expresión cartesiana “cogito ergo sum” desde el punto de vista las lógicas tradicional y moderna. La expresión se muestra como un entimema con la premisa mayor omitida. Dos formas de interpretar la premisa mayor son claras: 1) como una afirmación convencional (la visión más aceptada entre los filósofos), 2) como una proposición que contiene una equivalencia. Se demuestra que la equivalencia de “pensar y ser” asumida por Descartes una vez abierta la oportunidad lógico-antropológica para proclamar como “no existente” lo no pensante. La última afirmación es la base del fundamentalismo racionalista. El trabajo demuestra que el análisis del entimema cartesiano se refiere directamente a nuestra comprensión de la condición ontológica del ser humano y es inseparable de la cuestión de la ética biomédica

Jet-induced gauge field instabilities in the quark-gluon plasma: A kinetic theory approach

We discuss the properties of the collective modes of a system composed by a thermalized quark-gluon plasma traversed by a relativistic jet of partons. The transport equations obeyed by the components of the plasma and of the jet are studied in the Vlasov approximation. Assuming that the partons in the jet can be described with a tsunami-like distribution function we derive the expressions of the dispersion law of the collective modes. Then the behavior of the unstable gauge modes of the system is analyzed for various values of the velocity of the jet, of the momentum of the collective modes and of the angle between these two quantities. We find that the most unstable modes are those with momentum orthogonal to the velocity of the jet and that these instabilities appear when the velocity of the jet is higher than a threshold value, which depends on the plasma and jet frequencies. The results obtained within the Vlasov approximation are compared with the corresponding results obtained using a chromohydrodynamical approach.The effect we discuss here suggests a possible collective mechanism for the description of the jet quenching phenomena in heavy ion collisions.Comment: 13 pages, 6 figure

Why Cannot the Theory of the Infinite Universe be Realized?

El presente trabajo demuestra que todas las teorías cosmológicas obedecen a una relación epistemológica : todos los pasos que hace la cosmología orientados a la adquisición de la condición de la ciencia natural es inversamente proporcional a sus pasos en la dirección de permitir valores infinitos de características cosmológicas. Analíticamente, la cosmología topó por primera vez con el problema del infinito cuando trata de explicar la rotación de la Tierra en los modelos antiguos. Un intento de introducir el infinito en la descripción del Universo según el modelo de Newton, dio lugar a las paradojas de la fotometría y la gravedad. La cosmología relativista, para eliminar las paradojas, ha tenido que otorgar una vez más características infinito del universo. La misma dificultad estética de los escenarios inflacionarios y caóticos.The present work demonstrates that all cosmological theories obey an epistemological relation: all steps cosmology makes in the direction of acquiring the status of a natural science are inversely proportional to its steps in the direction of allowing infinite values of cosmological features. Analytically, cosmology first encountered the problem of infinity when it tried to explain the rotation of the Earth in ancient models. An attempt to introduce infinity into the Universe description by the Newtonian model, resulted in the photometric and gravitational paradoxes. To eliminate the paradoxes, relativistic cosmology had to introduce once more the infinite characteristics of the Universe. The same difficulty is typical of the inflationary and chaotic scenarios

Cogito, ergo sum : from an enthymeme to bioethics

The work analyzes the Cartesian expression "cogito ergosum" from the points of view of the traditional and the modern logics. The expression is shown to be an enthymeme with the major premise omitted. Two ways of the major premise interpretation are made clear: 1) as a conventional assertion (a most commonly accepted view among philosophers); 2) as a proposition containing an equivalence. It is shown that the equivalence of "thinking and being" assumed by Descartes has once opened up the logical-anthropological opportunity to proclaim as "non-existing" what does not think. The last assertion provides the basis of "Ratiofundamentalism". The work demonstrates that the Cartesian enthymeme analysis concerns directly our understanding of the ontological status of man and is inseparable from the questions of biomedical ethics.El trabajo analiza la expresión cartesiana "cogito ergo sum" desde el punto de vista las lógicas tradicional y moderna. La expresión se muestra como un entimema con la premisa mayor omitida. Dos formas de interpretar la premisa mayor son claras: 1) como una afirmación convencional (la visión más aceptada entre los filósofos), 2) como una proposición que contiene una equivalencia. Se demuestra que la equivalencia de "pensar y ser" asumida por Descartes una vez abierta la oportunidad lógico-antropológica para proclamar como "no existente" lo no pensante. La última afirmación es la base del fundamentalismo racionalista. El trabajo demuestra que el análisis del entimema cartesiano se refiere directamente a nuestra comprensión de la condición ontológica del ser humano y es inseparable de la cuestión de la ética biomédica

Crossover between mean-field and Ising critical behavior in a lattice-gas reaction-diffusion model

Lattice-gas models for CO oxidation can exhibit a discontinuous nonequilibrium transition between reactive and inactive states, which disappears above a critical CO-desorption rate. Using finite-size-scaling analysis, we demonstrate a crossover from Ising to mean-field behavior at the critical point, with increasing surface mobility of adsorbed CO or with decreasing system size. This behavior is elucidated by analogy with that of equilibrium Ising-type systems with long-range interactions.Comment: 6 pages, 3 figure