Theory of Lattice and Electronic Fluctuations in Weakly Localized Spin-Peierls Systems

A theoretical approach to the influence of one-dimensional lattice fluctuations on electronic properties in weakly localized spin-Peierls systems is proposed using the renormalization group and the functional integral techniques. The interplay between the renormalization group flow of correlated electrons and one-dimensional lattice fluctuations is taken into account by the one-dimensional functional integral method in the adiabatic limit. Calculations of spin-Peierls precursor effects on response functions are carried out explicitely and the prediction for the temperature dependent magnetic susceptibility and nuclear relaxation is compared with available experimental data for (TMTTF)$_{2}$PF$_{6}$.Comment: 15 pages, 7 Encapsulated Postscript figure

On the Origin of the Anomalous Upper Critical Field in Quasi-One-Dimensional Superconductors

Upper critical field, H_c2, in quasi-1D superconductors is investigated by the weak coupling renormalization group technique. It is shown that H_c2 greatly exceeds not only the Pauli limit, but also the conventional paramagnetic limit of the Flude-Ferrell-Larkin-Ovchinnikov (FFLO) state. This increase is mainly due to quasi-1D fluctuations effect as triggered by interference between unconventional superconductivity and density-wave instabilities. Our results give a novel viewpoint on the large H_c2 observed in TMTSF-salts in terms of a d-wave FFLO state that is predicted to be verified by the H_c2 measurements under pressure.Comment: 5 pages, 4 figure

Mécanique quantique III

Troisième cours de mécanique quantique à l'Université de Sherbrooke. Contenu : Spin de l’électron, Composition du moment cinétique, Méthodes d’approximation en mécanique quantique, Particules identiques, Molécules, Théorie des perturbations dépendantes du temps, Introduction à la théorie de la diffusion

Méthodes de physique théorique

Cours sur certains outils mathématiques de la physique à l'Université de Sherbrooke: variables complexes (fonctions analytiques, théorème du résidu, séries, transformation de Hilbert, méthode du col) et équations différentielles aux dérivées partielles (séparation des variables, problème de Sturm-Liouville, fonctions spéciales)

Symétries brisées et états cohérents de la matière

Ressources éducatives libresOpen educational resourcesCours de niveau MSc ou PhD à l'Université de Sherbrooke. Contenu : Magnétisme, Ensembles statistiques, Introduction aux transitions de phase, Seconde quantification, Bosons, Supraconductivité

Microwave dielectric study of spin-Peierls and charge ordering transitions in (TMTTF)2_2PF6_6 salts

We report a study of the 16.5 GHz dielectric function of hydrogenated and deuterated organic salts (TMTTF)$_2$PF$_6$. The temperature behavior of the dielectric function is consistent with short-range polar order whose relaxation time decreases rapidly below the charge ordering temperature. If this transition has more a relaxor character in the hydrogenated salt, charge ordering is strengthened in the deuterated one where the transition temperature has increased by more than thirty percent. Anomalies in the dielectric function are also observed in the spin-Peierls ground state revealing some intricate lattice effects in a temperature range where both phases coexist. The variation of the spin-Peierls ordering temperature under magnetic field appears to follow a mean-field prediction despite the presence of spin-Peierls fluctuations over a very wide temperature range in the charge ordered state of these salts.Comment: 7 pages, 6 figure