Hubbard Model

Superconductivity in the Attractive Hubbard Model

This work is done with A. Sewer, H. Beck and with the following external collaborations:

Xenophon Zotos, IRRMA, Ecole Polytechnique Fédérale, Lausanne (zotos@irrma.epfl.ch)

Daniel Ariosa, Département de Physique, Ecole Polytechnique Fédérale, Lausanne (ariosa@dpmail.epfl.ch)

Toni Schneider, Physics Department, University of Zürich (toni.schneider@swissonline.ch)

Jose-Jesus Rodriguez, Universidade Federal de Santa Maria, Rio deJaneiro (jjrn@einstein.sf.dfis.furg.br)

We study models with different types of interaction (attraction between electrons on the same or on nearest neighbor sites, possibly combined with on-site or long range repulsion) by functional integral techniques, by the T-matrix approximation and by Quantum Monte Carlo simulations.

The following aspects are treated:

Manifestations of the fluctuations of the superconducting order parameter above the transition temperature (in particular: pseudo-gap in the one-electron density of states, diamagnetic susceptibility, specific heat, transport coefficients)

Interplay and competition between different types of fluctuations leading to antiferromagnetic, charge density wave or superconducting instabilities.

Recent Publications:

From BCS-like superconductivity to condensation of local pairs: a numerical study of the attractive Hubbard model

Superconducting properties of the attractive Hubbard model
M.H.Pedersen, J.J.Rodriguez-Nunez, H.Beck, T.Schneider, S.Schafroth; Zeitschrift für Physik B 103, 21-28 (1997)

Screening effects in superconductors

One-electron spectral functions of the attractive Hubbard model for intermediate coupling
M.Y. Kagan, R.Frésard, M.Capezzali, H.Beck; Phys Rev B 57, 5995 (1998)

Pseudogap, Quantum Phase Fluctuations and Spectroscopy of HTCS Cuprates
D. Ariosa, H. Beck, M. Cappezzali; Journal of Physics and Chemistry of Solids, in press

Evolution of single-particle Green functions with correlation in the Hubbard model at half-filling: sum rules for the spectral density
J.J.Rodriguez-Nunez, S.Schafroth, H.Beck; Physica B 259-261, 773 (1999)

One-electron Green function for the Hubbard model including next nearest neighbor hopping,
R.Kirchhofer, R.Frésard, H.Beck, J.J.Rodriguez-Nunez; Physica B 259-261, 775 (1999)

Pseudogap in the one-electron spectral functions of the attractive Hubbard model,
M. Capezzali, H.Beck; Physica B 259-261, 501 (1999)

Orbital magnetic susceptibility of the attractive Hubbard model,
A.Sewer, H.Beck, X.Zotos; Physica C317-318, 475 (1999)

Excitation spectrum of the two-dimensional attractive Hubbard model
M.Capezzali, H.Beck;, Physica C317-318, 482 (1999)

PhD Thesis

Superconductivity in two Dimensions: Spectral Properties of the Attractive Hubbard Model and Dynamics of Vortices
Massimiliano Capezzali (1998)

The Hubbard Model with Attractive Nearest Neighbor Interaction

Diploma Thesis

Différentes études d'instabilités d'un modèle de Hubbard attractif généralisé
Matthieu Karrer (2001)

Modèle de Hubbard étendu avec U répulsif et W attractif et transition de Mott
Roland Kirchhofer (1997)