Ground state structure and excitations in strongly correlated Fermi systems

Klaus Osterloh, N. Barberán, Maciej Lewenstein

We study strongly correlated ground and excited states of rotating quasi-2D Fermi gases constituted of a small number of dipole-dipole interacting particles with dipole moments polarized perpendicular to the plane of motion. As the number of atoms grows, the system enters an intermediate regime, where ground states are subject to a competition between distinct bulk-edge configurations. This effect obscures their description in terms of composite fermions and leads to the appearance of novel quasihole ground states. In the presence of dipolar interactions, the principal Laughlin state at filling nu=1/3 exhibits a substantial energy gap for neutral (total angular momentum conserving) excitations and is well-described as an incompressible Fermi liquid. Instead, at lower fillings, the ground state structure favors crystalline order.

T. V. Ramakrishnan, B. Sriram Shastry

Takaaki Sogo, Takahiko Miyakawa, T. Suzuki +1 more

Collective excitations of a trapped Bose–Fermi mixture of atomic gases are studied in a random-phase approximation. Density profiles in the ground states are solved in the mean field approximation for various strengths of Bose–Fermi interaction. Monopole strength distributions and the dynamical structure factors are investigated for two types of the Bose–Fermi mixture. It is found in the mixture with the large excess of bosons the fermionic strength is concentrated in a single collective state for strong Bose–Fermi interactions. The dynamical structure factors for these collective states show that fermions are correlated through the Bose condensate. Time dependent behavior of the system after an external impulse is also studied.

M. Ya. Amusia, Vasily R. Shaginyan

G E Astrakharchik, J Boronat, E. Krotscheck +1 more

We present a theoretical study of the dynamic structure function of a resonantly interacting two-component Fermi gas at zero temperature. Our approach is based on dynamic many-body theory able to describe excitations in strongly correlated Fermi systems. The fixed-node diffusion Monte Carlo method is used to produce the ground-state correlation functions which are used as an input for the excitation theory. Our approach reproduces recent Bragg scattering data in both the density and the spin channel. In the BCS regime, the response is close to that of the ideal Fermi gas. On the BEC side, the Bose peak associated with the formation of dimers dominates the density channel of the dynamic response. When the fraction of dimers is large our theory departs from the experimental data, mainly in the spin channel.

Sadamichi Maekawa