The Compressibility at Unitarity: A Superfluid Signature in Trapped Ultracold Fermi Gases

The behavior of the thermodynamic compressibility of a trapped ultracold Fermi gas at unitarity is explored as the temperature approaches the critical temperature and the gas undergoes a phase transition to a superfluid state. This phase transition offers an opportunity to probe the microscopic underpinnings of this transition and can serve as a test of theoretical approaches. In this study, the collective behavior of the gas as it undergoes this phase transition is described using normal modes. The Pauli principle is applied “on paper” using specific normal mode assignments that are consistent with this fundamental principle. This study finds a small signature of the transition at the critical temperature in contrast to previous experimental and theoretical results.