Unlike their bosonic counterparts, fermionic condensates (such as superconductors, superfluid Helium 3 or two-component Fermi gases) are made of composite objects: the Cooper pairs. This underlying composite structure gives them a rich excitation spectrum: besides the phononic (in neutral systems) or plasmonic branch (in charged systems) of density excitations, fermionic condensates support a collective branch corresponding to a vibration of the binding energy of the Cooper pairs. At low temperature, this mode (sometimes reductively called a Higgs mode) can be observed with ultracold gases by tuning the interaction strength, and tracking the decaying oscillations of the order parameter. Near the critical temperature, the mode evolves into a low-energy pairing mode of quadratic dispersion, which (above Tc) acts as a precusor of the phase transition.
Host: Nir Navon (nir.navon@yale.edu)