Research Activity

The main research activity of the Quantum Gases Theory group led by Prof. G. C. Strinati concerns the physics of ultracold atomic Fermi gases. These systems have emerged in the last few years as prototypes for studying many-body effects throughout the BCS-BEC crossover. Here, the mutual effective fermionic attraction can be varied essentially at will by spanning a Fano-Feshbach resonance via an applied magnetic field. This ability enables the system to pass from the weak-coupling (BCS) situation with largely overlapping Cooper pairs, to the strong-coupling (BEC) limit where composite bosons form and condense. The importance of this study stems also from the fact that advances in the fundamental knowledge, obtained from the study of the BCS-BEC crossover with ultracold Fermi gases, might also have implications for other physical systems (notably, high-Tc superconductors and nuclear matter).

The main theoretical concern of the BCS-BEC crossover is the evolution of the physical properties of a system of interacting fermions when passing from weak to strong attraction, whereby the evolution has to be described within the framework of a single fermionic theory. For weak attraction and sufficiently low temperatures, the system enters the superfluid phase which is well described by the standard (BCS) theory of superconductivity. In this limit, the temperatures of formation and condensation of the Cooper pairs coincide. For strong attraction, tightly-bound composite bosons instead form and condense at sufficiently low temperature (BEC), in such a way that the condensation temperature can be much lower than the formation temperature.

The theoretical approach of the Camerino group is based on the use of a many-body Hamiltonian for two fermionic species mutually interacting via a contact potential. The use of a single-channel Hamiltonian for the BCS-BEC crossover with ultracold atoms can be actually justified from first principles both for 6Li and 40K. The single-channel Hamiltonian for fermions interacting via a contact potential offers definite advantages, due to some simplifying features in the many-body approach occurring with this model.

The Camerino group has made several contributions to the physics of the BCS-BEC crossover over the past several years, based on a judicious use of many-body diagramatic techniques at finite temperature. These contributions are summarized in the list of publications reported below.

Several other topics are currently under investigation by the Camerino group, which include:

The Josephson effect in the BCS-BEC crossover;
Pairing effects in two-dimensional systems;
Pairing in Bose-Fermi mixtures;
The effects of disorder on the BCS-BEC crossover;
Superfluidity in bilayer systems;
Multiband superconductors;
The vortices in the BCS-BEC crossover.

A movie showing the self-assembling of a vortex lattice in a Fermi gas under rotation, as obtained through the numerical solution of the LPDA equation recently introduced by our group, is available here.