Atomic, Molecular, and Optical Physics Seminar

Superfluidity and Pairing in a Strongly-Interacting Imbalanced Fermi Gas

Dr. Yong-Il Shin
Physics Department
MIT

Fermionic superfluidity with imbalanced spin populations has been an intriguing problem for many decades. Cooper pairing is the underlying mechanism for the conventional Bardeen-Cooper-Schrieffer (BCS) superfluid state of equal mixture of two fermionic components. However, population imbalance between the two components distresses the fully-paired state, eventually leading to the breakdown of superfluidity. This is known as the Chandrasekhar-Clogston (CC) limit. We have experimentally investigated the superfluid and normal phases of a population-imbalanced Fermi gas in a strongly interacting regime. We have observed that an imbalanced Fermi mixture maintains superfluidity up to a critical imbalance, showing the CC limit of superfluidity. The superfluid region in the imbalanced mixture was found to have equal densities of the two components and spatially separate from a normal region with unequal densities. Rf-spectroscopy was used to study the pairing in the strongly-interacting normal phase. Surprisingly, we have observed full pairing of the minority component in the normal phase even above the critical imbalance. This clearly demonstrates that mismatched Fermi surfaces do not prevent pairing but quench the superfluid state, thus realizing a system of fermion pairs that do not condense even at the lowest temperature. I will discuss the phase diagram of an imbalanced Fermi mixture based on our experimental observations.

Monday, February 19, 2007
4:00 pm
Gant Science Complex
Physics Department
Room P121


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