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11:00» Seminaire LPTMS: Alexander Ossipov (Nottingham) 
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11:00» Seminaire LPTMS:Olga Dimitrova (LPTMS) 
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14:30» Séminaire du LPTMS : Alessio Recati 
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11:00» Semianire LPTMS: Henk van Beijeren (Utrecht) 
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14:00» Séminaire PHYSTATSUD : Lev Ioffe 
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14:00» Séminaire commun LPT  LPTMS : Camille Aron 
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Multifractal eigenfunctions in random matrix ensembles
Alexander Ossipov, The University of Nottingham
Random matrix models is an efficient tool to study the Anderson metalinsulator transition. In this talk we focus on two such models: the powerlaw banded random matrices and the ultrametric random matrices. Using the weak disorder virial expansion we show how the
multifractal critical exponents can be calculated analytically.Relations between different critical exponents, universality of the results as well as some open problems are discussed.Mardi 4 mai à 11h
LPTMSbatiment 100, salle 201, Orsay
Infrared catastrophe in twoquasiparticle collision integral
Olga Dimitrova, LPTMS
Relaxation of a nonequilibrium state in a disordered metal with a spindependent electron energy distribution is considered. The collision integral due to the electronelectron interaction is computed within the approximation of a twoquasiparticle scattering. We show that the
spinflip scattering processes with a small energy transfer may lead to the divergence of the collision integral for a quasi onedimensional wire. This divergence is present only for a spindependent electron energy distribution which corresponds to the total electron spin magnetization M = 0 and only for nonzero interaction in the triplet channel. We found the infrared cutoff to be proportional to the inverse dephasing time by taking into account the corrections to the collision integral from the manyparticle processes.
Mardi 11 Mai à 11h
LPTMSbatiment 100, salle 201, Orsay
Bogoliubov theory of a dumbhole in BoseEinstein condensates and density correlation as a probe of analog "Hawking radiation"
Alessio Recati, CNRINO, BEC Center, University of Trento, Italie
Sonic analogous of black holes have been proposed in the 80's by B. Unruh. In these setups, the flow of a fluid becomes supersonic in some region of space, and no sound issued from the supersonic region can reach the subsonic one. One speaks of a dumb hole. Dumb holes have been considered as potential tools to get hints in black hole radiation which is a quantum effect predicted by S. Hawking in the 70's. Most of the analysis rely on a formal analogy between hydrodynamics in presence of a sonic horizon and quantum fields in curved spacetimes.
We apply the microscopic Bogoliubov theory to analyze the fluctuations of the flow of a dilute atomic condensate in the presence of a sonic horizon. We show that the densitydensity correlation has a peculiar longdistance behavior which represents a new and better way to detect what is called analog Hawking radiation. The analytical results are in good quantitative agreement with first principle numerical calculations.
Mercredi 12 Mai à 14h30
LPTMSbatiment 100, salle 201, Orsay
Exact solutions of TASEPs describing twoway traffic at several speeds
Henk van Beijeren, Utrecht
As shown by Karimipour[1] the Matrix Product Ansatz method for solving the totally asymmetric
exclusion process can be generalized to a system of several species of particles. For this to be
possible the following conditions must hold:
1) Define the free velocity vi of a particle of species i as plus or minus the exchange rate with an empty site to its right respectively to its left depending on the sign of vi . Then the exchange rate of a particle of type i with a particle of type j to its right must be vi − vj if vi − vj > 0 and zero otherwise.
2) Define i and i as the injection respectively extraction rate for species i, with injection on the left and extraction on the right for species of positive velocity and the other way around for species of negative sign. Then the extraction rates have to satisfy the conditions vi − vj = i − j if vi and vj have the same sign (in contrast to what is stated in [1] no conditions have to be imposed on the injection rates).
In a grand ensemble formalism one easily postulates a general form for the partition function with a few parameters that can be identified easily. From this one immediately obtains all the currents and densities as functions of the exchange, injection and extraction rates. Like in the 1species case, depending on these rates one will usually have at least three different phases, one determined by the injection and extraction rates on the left (the low density phase), one determined by the corresponding rates on the right (the high density phase) and one or more that depend only on ratio’s between injection rates (the maximum current phase in the onespecies system).
V. Karimipour, Phys. Rev. E 59 (1999) 205; M. Khorrami and V. Karimipour, J. Stat. Phys. 100
(2000) 999Mardi 18 mai à 11h
LPTMSbatiment 100, salle 201, Orsay
SuperconductorInsulator transition driven by disorder
Lev Ioffe (LPTMS, Rutgers University)
I will begin by reviewing the experimental data on the superconductorinsulator transition in InO, TiN and similar films. I will argue that the transition in these materials is driven entirely by the competition of the disorder and attraction. I will discuss the solution of the simplest mathematical model that has these ingredients and show that the resulting quantum critical point has many anomalous and unexpected features. The most striking feature of the solution is that the phase formed in the vicinity of the quantum critical point becomes very nonuniform and that it is this nonuniformity that is responsible for most physical properties. I will present very recent data from STM measurements that confirm some of the predictions of the theory.
Jeudi 20 mai à 14h
LPTMSbatiment 100, salle 201, Orsay
Driven Quantum Coarsening
Camille Aron ( Laboratoire de Physique Théorique et Hautes Énergies, Université Pierre & Marie Curie, Paris )
We solve the dynamics of an ensemble of disordered quantum rotors coupled to two leads at different chemical potential letting a current flow through the system and driving it out of equilibrium. We discuss the phase diagram in the temperature, voltage, strength of quantum fluctuations and coupling to the bath. We uncover the coarsening regime. In particular, the scaling functions of correlation and response at late epochs are proven to coincide with their classical counterparts.
Jeudi 27 Mai 2010 à 14h
LPT, Bâtiment 210, salle 114, Orsay