Physics Colloquium, April 14, 2009
High-Temperature Superfluidity in an Ultracold Fermi Gas of Atoms Martin W. Zwierlein

Massachusetts Institute of Technology

From quarks and electrons to Neutron stars, fermions, particles with half-integer spin, are the building blocks of matter. They organize under the influence of interactions, forming nuclei, atoms, high-temperature superconductors and quark superfluids. An ultracold gas of Lithium-6 atoms allows us to study fermions in a highly controllable environment. The interactions between atoms can be varied at will over an enormous range via Feshbach scattering resonances. In an equal mixture of spin up and spin down fermions with attractive interactions, atoms pair up and form a superfluid. By varying the interaction strength, we can study the crossover from a Bose-Einstein condensate of tightly bound molecules to a Bardeen-Cooper-Schrieffer superfluid of long-range Cooper pairs. Superfluidity in this crossover regime is demonstrated by setting the gas under rotation and observing ordered lattices of quantized vortices. Thanks to its strong interactions, the gas is a high-temperature superfluid: Scaled to the density of electrons in a metal, superfluidity would occur already far above room temperature. A new regime is entered when the number of spin up versus spin down atoms is imbalanced. In this case, not every spin up atom can find a spin down partner. The ground state of such a system has been under debate for over 40 years. We observe the breakdown of the superfluid at a critical imbalance, giving way to an intriguing, strongly interacting Fermi gas with unequal spin populations.

Dr. Zwierlein's Web Site

4:00 p.m., Physics Research Building (PRB), Room 1080

Reception at 3:45 p.m., Atrium, PRB