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SEMINARIO DFI: Non-linear transport in Kondo-correlated quantum dots: a dual fermion perturbation th |
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Expositor: Enrique Muñoz Tavera Expositor: Enrique Muñoz Tavera Departamento de Física P. Universidad Católica de Chile Viernes 5 de octubre, 16 h Av. Blanco Encalada 2008, tercer piso Sala de seminarios The non-linear conductance of semiconductor hetero-structures and single molecule devices exhibiting Kondo physics has recently attracted attention. We address the observed sample dependence across various systems by considering additional electronic contributions present in the effective low-energy model underlying these experiments. To this end, we develop a novel perturbation theory in terms of dual fermions on the Keldysh contour. We analyze the role of particle-hole asymmetry on the transport coefficients. Our approach systematically extends the work of Yamada and Yosida and others to the particle-hole asymmetric Anderson model out of equilibrium. It correctly describes the strong coupling physics and satisfies current conservation. Our approach is also extended to obtain analytical expressions for other transport coefficients, such as the thermal conductance and Seebeck coefficient beyond linear response. (1) E. Muñoz, C. J. Bolech and S. Kirchner. "Universal out-of-equilibrium transport in Kondo correlated quantum dots: renormalized dual fermions on the Keldysh contour". Phys. Rev. Lett. (2012, with referees). (2) S. Kirchner, F. Zamani and E. Muñoz, "Nonlinear thermoelectric response of quantum dots: renormalized dual fermions out of equilibrium". Chapter 10 in "New Materials for Thermoelectric Applications: Theory and Experiment". Springer (2012). V. Zlatic’ and A. Hewson (eds.), ISBN:9789400749832.
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SEMINARIO DFI: Waves on a foam surface: propagation of subshear and supershear pulses. |
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Expositor: Guillaume Lagubeau Física No Lineal, USACh Viernes 28 de Septiembre, 16 h Av. Blanco Encalada 2008, tercer piso Sala de Seminarios Liquid foams consist in a concentrated dispersion of gas bubbles in a continuous liquid phase. The dynamical properties of such a mixture, studied by rheologists over the last 30 years, are now well characterized, although not fully understood. Acoustics as a way to probe foam fast dynamics is a developing tool, that has to face the challenge of the strong dissipation occurring in this medium and therefore requires highly accurate measurement methods. Taking advantage of the precision of a space-time resolved profilometry technique we present here the first foam study using surface acoustics. Subsequently, we observe two kinds of surfaces waves: the well known anelastic Rayleigh wave and a supershear surface wave that can be identified with another solution of Rayleigh’s secular equation. |
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Seminario DFI: Bacterias interactuando con oxígeno |
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Expositora: Jocelyn Dunstan Escudero Department of Applied Mathematics and Theoretical Physics, University of Cambridge, UK Viernes 7 de septiembre, 16 h Av Blanco Encalada 2008, tercer piso Sala de Seminarios La produccion de luz por organismos vivos se conoce como bioluminiscencia. Un ejemplo de este fenomeno lo constituye la bacteria marina Photobacterium phosphoreum, la cual requiere oxígeno para producir fotones. Cuando una suspensión de esta bacteria se observa en una celda vertical, una interesante inestabilidad hidrodinámica aparece. Experimentos en dos dimensiones, junto con un modelo complementado con simulaciones numéricas, nos permiten tener una idea de la relación entre emisión de luz y el consumo de oxígeno. Además, se presenta otro experimento, esta vez usando la bacteria Escherichia coli, y en donde la presencia de oxigeno permite generar motilidad en la bacteria. A pesar de las diferencias entre estos dos sistemas, se propone un modelo que explicaría ambos fenómenos. |
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Seminario Magnetismo: Spin caloritronics – more than spin-dependent thermoelectrics |
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Expositor: Gerrit E.W. Bauer Institute of Materials Researh, Tohoku University, Japan, and Kavli Institute of NanoScience, TU Delft, The Netherlands, Lunes 3 de Septiembre, 16:00 hrs. Av Blanco Encalada 2008, tercer piso Sala de Seminarios, DFI, FCFM, Universidad de Chile The spin degree of freedom of the electron affects not only charge, but also heat and thermoelectric transport, leading to new effects in small structures that are studied in the field of spin caloritronics (from calor, the Latin word for heat). This lecture addresses the basic physics of spin caloritronics. Starting with an introduction into thermoelectrics and Onsager’s reciprocity relations, the generalization to include the spin dependence in the presence of metallic ferromagnets will be addressed. Using this foundation I will describe several recently discovered spin-dependent effects in metallic nanostructures and tunneling junctions in terms of a two spin-current model of non-interacting. Next, I will argue that a different class of spin caloritronic effects exists that can be explained only by the collective spin dynamics in ferromagnets. The thermal spin transfer torque that allows excitation and switching of the magnetization in spin valves as well as the operation of nanoscale heat engines is complemented by thermal spin pumping. The latter generates the so-called spin Seebeck effect, which is generated by a heat current-induced non-equilibrium of magnons at a contact between an insulating or conducting ferromagnet and a normal metal. Under these conditions a net spin current is injected or extracted from the normal metal that can be detected by the inverse spin Hall effect. Both classes of effects can be understood in the adiabatic approximation for the magnetization dynamics and computed in terms of material-dependent electronic structures. Further issues to be addressed are the relation between electric, thermal and acoustic actuation of the magnetic order parameter, as well as the application potential of spin caloritronics. More details and a bibliography can be found in Ref. [1]. [1] G.E.W. Bauer, E. Saitoh, and B.J. van Wees, Spin Caloritronics, Nature Materials 11, 391 (2012). |
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