Volume 79, Number 5, September 2007
Article Number 50003
Number of page(s) 6
Section General
Published online 08 August 2007
EPL, 79 (2007) 50003
DOI: 10.1209/0295-5075/79/50003

Tightly bound gap solitons in a Fermi gas

S. K. Adhikari1 and B. A. Malomed2

1  Instituto de Física Teórica, UNESP - São Paulo State University - 01.405-900 São Paulo, São Paulo, Brazil
2  Department of Physical Electronics, School of Electrical Engineering, Faculty of Engineering, Tel Aviv University - Tel Aviv 69978, Israel

received 12 February 2007; accepted in final form 18 July 2007; published September 2007
published online 8 August 2007

Within the framework of the mean-field hydrodynamic model of a degenerate Fermi gas (DFG), we study, by means of numerical methods and variational approximation (VA), the formation of fundamental gap solitons (FGSs) in a DFG (or in a BCS superfluid generated by weak interaction between spin-up and spin-down fermions), which is trapped in a periodic optical-lattice (OL) potential. An effectively one-dimensional (1D) configuration is considered, assuming strong transverse confinement; in parallel, a proper 1D model of the DFG (which amounts to the known quintic equation for the Tonks-Girardeau gas in the OL) is considered too. The FGSs found in the first two bandgaps of the OL-induced spectrum (unless they are very close to edges of the gaps) feature a (tightly bound) shape, being essentially confined to a single cell of the OL. In the second bandgap, we also find antisymmetric tightly bound subfundamental solitons (SFSs), with zero at the midpoint. The SFSs are also confined to a single cell of the OL, but, unlike the FGSs, they are unstable. The predicted solitons, consisting of $\sim 10^{4}\hbox{--} 10^{5}$ atoms, can be created by available experimental techniques in the DFG of 6Li atoms.

03.75.Ss - Degenerate Fermi gases .
03.75.Lm - Tunneling, Josephson effect, Bose-Einstein condensates in periodic potentials, solitons, vortices, and topological excitations .
05.45.Yv - Solitons .

© Europhysics Letters Association 2007