Degenerate Fermi Gas Studied in Three-Dimensional Optical Lattice

A team of physicists at the Swiss Federal Institute of Technology in Zurich, Switzerland, has loaded a degenerate Fermi gas into a three-dimensional optical lattice and studied its response to changes in the strength of the trapping lasers and of an external magnetic field. The ability to confine degenerate fermions and to control the strength of their interaction has implications in the study of a wide variety of material systems, including high-temperature superconductors. A report of the group's work appears in the March 4 issue of Physical Review Letters.

The investigators employed a modified setup that they had used to study optically confined bosonic atoms to create and trap thousands of degenerate fermionic potassium-40 atoms in a lattice formed by three crossed standing waves from 826-nm lasers.

Fermions have spins that are an odd multiple of 1/2, and they begin to avoid each other and to fill all possible quantum energy levels as their temperature falls. Once loaded, the intensities of the laser beams and the magnetic field were varied to control filling of the lattice, transition from a normal state to a band insulator, interactions between spin states and coupling between energy bands.

In the image, the sharp-edged pillar in front is a filled first Brillouin zone in the cubic crystal structure of the optical lattice. The physicists obtained the experimental data rendered here by absorption imaging of the fermionic gas after adiabatic release from the lattice.