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Etude numérique de systèmes magnétiques et supraconducteurs

Fabien Alet 1
1 Groupe de Physique Théorique (LPQ)
LPQ - Laboratoire de Physique Quantique
Abstract : In this thesis, we study magnetic or superconducting phases of various models representative of strongly correlated systems. These studies have all been conducted by numerical ways, with the help of non-local Monte Carlo algorithms. First of all, two Quantum Monte Carlo algorithms (the loop algorithm and the Stochastic Series Expansion), considered as the most sophisticated at the present time, are explained in details. We then consider quantum spin 1 systems. Firstly, we study, in direct relation with experiments, the numerical reconstruction of Nuclear Magnetic Resonance spectra of Haldane chains doped with non magnetic impurities. The results of this study are in very good agreement with the experimental spectra obtained on the compound Y_2BaNi_{1-x}Mg_xO_5. Secondly, we study the quantum phase transition taking place in weakly coupled Haldane chains with the help of a new self-adapting method. With this numerical method, we obtain with high precision and modest effort the value of the interchain coupling necessary to order antiferromagnetically the system. Finally, the last part of this thesis introduces a new non-local Quantum Monte carlo algorithm called "worm algorithm'', used for the study of the bosonic Hubbard model in the phase approximation. Its great efficiency, caracterized by a dynamical exponent z=0.3(1) very small, is demonstrated with high precisions simulations for the value mu=0 of chemical potential. Furthermore, an explicit demonstration of detailed balance for this algorithm is given.
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Contributor : Fabien Alet <>
Submitted on : Wednesday, January 15, 2003 - 9:30:34 PM
Last modification on : Friday, February 28, 2020 - 1:57:38 PM
Long-term archiving on: : Tuesday, September 11, 2012 - 7:25:11 PM


  • HAL Id : tel-00002275, version 1



Fabien Alet. Etude numérique de systèmes magnétiques et supraconducteurs. Matière Condensée [cond-mat]. Université Paul Sabatier - Toulouse III, 2002. Français. ⟨tel-00002275⟩



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