Influence des impuretes et du desordre dans des systemes magnetiques de basse dimensionnalite

Abstract : In strongly correlated systems, such as copper oxydes, the interplay between quantum fluctuations and disorder can gives rise to a non trivial new physics. In order to achieve a good understanding of the peculiarity of impurities and disorder effects in low dimensionnal magnets, numerical tools have been intensively used during this PhD thesis. First, we will see that the behavior of finite size antiferromagnetic spin-1/2 chains with bond randomness is controlled by a crossover between a critical line of pure fixed points and an infinite randomness fixed point. Interestingly enough, a direct analogy with localization in one dimension will be discussed through the existence of only one relevant disorder dependent lenght scale which governs both phenomenon. In addition, we also deal with disorder effects in spin gapped systems through the problem of doping coupled frustrated spin-1/2 chains with non magnetic impurities, in order to describe the properties of the spin-Peierls compound CuGeO3 under doping. An effective low energy hamiltonian, which describes the interaction between impurities under the spin gap, is derived and studied with SSE quantum Monte Carlo simulations in order to investigate the impurity-induced antiferromagnetic ordering mechanism. The rest of the work is devoted to the unexpected behavior of the low temperature magnetic susceptibility which is understood with a real space renormalization group approach. Critical properties of this quasi-one dimensionnal system will be compared with previously known random magnets universality classes.
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https://tel.archives-ouvertes.fr/tel-00006529
Contributor : Nicolas Laflorencie <>
Submitted on : Tuesday, July 20, 2004 - 6:04:22 PM
Last modification on : Friday, October 11, 2019 - 8:22:44 PM
Long-term archiving on : Friday, April 2, 2010 - 8:19:30 PM

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Nicolas Laflorencie. Influence des impuretes et du desordre dans des systemes magnetiques de basse dimensionnalite. Matière Condensée [cond-mat]. Université Paul Sabatier - Toulouse III, 2004. Français. ⟨tel-00006529⟩

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