PAIR EXCITATIONS IN THE GROUND-STATE OF A 2-DIMENSIONAL ATTRACTIVE FERMI GAS

M. B. Vetrovec

M. Ya. Amus’ya

No author provided

The excitation spectrum of pair fluctuations in the ground state of a dilute two-dimensional (2D) attractive Fermi-gas is studied for different coupling regimes. In the strong-coupling limit the spectrum has the Bogolubov form, but in the weak-coupling regime there are two types of the pair excitations (different from two-fermion scattering states): (i) long-wavelength collective mode with the cutoff at momentum q(c) similar to 1/xi(0), where xi(0) is the pair size, and (ii) pair excitations with q greater than or equal to root 8m mu.

Sergei V. Traven

P. Schlottmann, Andrei A. Zvyagin

In the context of ultracold atoms with effective spin S = 5/2 confined to an elongated trap we study the one-dimensional Fermi gas interacting via an attractive δ-function potential using the Bethe ansatz solution. There are N = 2S + 1 = 6 fundamental states: The particles can either be unpaired or clustered in bound states of 2, 3, …, 2S and 2S + 1 fermions. The rich ground state phase diagram consists of these six states and various mixed phases in which combinations of the fundamental states coexist. Possible scenarios for phase separation due to the harmonic confinement along the tube are explored within the local density approximation. In an array of tubes with weak Josephson tunneling superfluid order may arise. The response functions determining the type of superfluid order are calculated using conformal field theory and the exact Bethe ansatz solution. They consist of a power law with distance times a sinusoidal term oscillating with distance. The wavelength of the oscillations is related to the periodicity of a generalized Fulde–Ferrell–Larkin–Ovchinnikov (FFLO) state.

Bernd Fröhlich