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

Quasi one-dimensional organic conductors: from Fr\"ohlich conductivity and Peierls insulating state to magnetically-mediated superconductivity, a retrospective

It is indisputable that the search for high-temperature superconductivity has stimulated the work on low-dimensional organic conductors at its beginning. Since the discovery of true metal-like conduction in molecular compounds more than 50 years ago, it appeared that the chemical composition and the quasi one-dimensional crystalline structure of these conductors were determining factors for their physical properties; materials with incommensurate conduction band filling favoring the low-dimensional electron-phonon diverging channel and the establishment of the Peierls superstructure and more rarely superconductivity at low temperature, while those with commensurate band filling favor either magnetic insulating or superconducting states depending on the intensity of the coupling between conductive chains. In addition, the simple structures of these materials have allowed the development of theoretical models in close cooperation with almost all experimental findings. Even though these materials have not yet given rise to true high-temperature superconductivity, the wealth of their physical properties makes them systems of choice in the field of condensed matter physics due to their original properties and their educational qualities. Research efforts continue in this field. The present retrospective, which does not attempt to be an exhaustive review of the field, provides a set of experimental findings alluding to the theoretical development while a forthcoming article will address in more details the theoretical aspect of low dimensional conductors and superconductors.Comment: 96 pages, 131 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