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Theses

Echelles de spins dopées sous champ magnétique

Guillaume Roux 1
1 FFC - Fermions Fortement Corrélés (LPT)
LPT - Laboratoire de Physique Théorique
Abstract : This thesis deals with the physics of doped two-leg ladders which are a quasi one-dimensional and unconventional superconductor. We particularly focus on the properties under magnetic field. Models for strongly correlated electrons on ladders are studied using exact diagonalization and density-matrix renormalization group (DMRG). Results are also enlightened by using the bosonization technique. Taking into account a ring exchange highlights the relation between the pairing of holes and the spin gap. Its influence on the dynamics of the magnetic fluctuations is also tackled. Afterwards, these excitations are probed by the magnetic field by coupling it to the spin degree of freedom of the electrons through Zeeman effect. We show the existence of doping-dependent magnetization plateaus and also the presence of an inhomogeneous superconducting phase (FFLO phase) associated with an exceeding of the Pauli limit. When a flux passes through the ladder, the magnetic field couples to the charge degree of freedom of the electrons via orbital effect. The diamagnetic response of the doped ladder probes the commensurate phases of the t-J model at low J/t. Algebraic transverse current fluctuations are also found once the field is turned on. Lastly, we report numerical evidences of a molecular superfluid phase in the spin-3/2 attractive Hubbard model: at a density low enough, bound states of four fermions, called quartets, acquire dominant superfluid fluctuations. The observed competition between the superfluid and density fluctuations is connected to the physics of doped ladders.
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https://tel.archives-ouvertes.fr/tel-00167129
Contributor : Guillaume Roux <>
Submitted on : Wednesday, August 15, 2007 - 12:39:44 PM
Last modification on : Thursday, February 27, 2020 - 4:40:05 PM
Long-term archiving on: : Thursday, April 8, 2010 - 9:17:44 PM

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  • HAL Id : tel-00167129, version 1

Citation

Guillaume Roux. Echelles de spins dopées sous champ magnétique. Supraconductivité [cond-mat.supr-con]. Université Paul Sabatier - Toulouse III, 2007. Français. ⟨tel-00167129⟩

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