Quantum Institute: Visitor Schedule

The Quantum Lunch is regularly held on Thursdays in the Theoretical Division Conference Room, TA-3, Building 123, Room 121.
For more information, contact Diego Dalvit.

March 30, 2006
12:30 PM

Randy Hulety,
Rice University

Paring and Phase Separation in a Polarized Fermi Gas

Abstract

In the conventional theory of superconductivity, pairing occurs only when the Fermi energies of the two spin-components are equal. There has been great interest, however, in the consequences of mismatched Fermi energies that may arise in several important situations, including magnetized superconductors and cold dense quark matter at the core of neutron stars. Pairing is qualitatively altered by the Fermi energy mismatch, and there has been considerable speculation regarding the nature and relative stability of various proposed exotic phases. We have explored this situation experimentally by creating a two-component gas of ⁶Li atoms where the relative Fermi energies are altered by changing the relative numbers of each component [1]. The BEC-BCS crossover with tunable interactions is realized via a Feshbach resonance. We observe that above a critical polarization the gas separates into a paired core surrounded by a shell of the excess unpaired atoms (see figure). Below the critical polarization the gas accommodates the excess atoms, and remarkably, does not measurably alter the interaction energy of a fully paired gas. The nature of this polarized, yet apparently superfluid phase remains to be explored. I will discuss this experiment and related investigations of the BEC-BCS crossover in ultracold atomic gases.

[1] G. B. Partridge et al., Science 311, 503 (2006).