Condensed Matter Seminar Series

Götz Seibold

Brandenburgische Technische Universität

Dynamical properties of strongly correlated condensates

We analyze the dynamics of strongly coupled superconductors from the BCS to the BEC regime, with a particular focus on the amplitude (“Higgs”) mode. While in the weak coupling limit we find that the amplitude fluctuations are short-lived due to a degeneracy with the energy of the edge of the quasiparticle continua (and in agreement with Hartree-Fock + RPA theory), these are shifted below the edge upon increasing the interaction. Our calculations therefore predict undamped amplitude (Higgs) oscillations of the order parameter in strongly coupled superconductors, cold atomic fermion condensates and in strongly interacting charge- and spin-density wave systems. 

The approach also allows to study the non-equilibrium situation relevant for pump probe experiments. We find a crossover from the BCS dynamics to a new strong coupling regime where a characteristic frequency U, associated to double occupancy fluctuations controls the order parameter dynamics. The change of regime occurs close to a dynamical phase transition which is characterized by a complex structure of self-driven slow Rabi oscillations.