Bulletin of the American Physical Society
38th Annual Meeting of the Division of Atomic, Molecular, and Optical Physics
Volume 52, Number 7
Tuesday–Saturday, June 5–9, 2007; Calgary, Alberta, Canada
Session Q1: Strongly Correlated Fermions |
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Chair: P. Engels, Washington State University Room: TELUS Convention Centre Macleod D |
Friday, June 8, 2007 1:30PM - 2:06PM |
Q1.00001: Thermodynamic Measurements in a Strongly Interacting Fermi Gas Invited Speaker: The thermodynamics of strongly interacting Fermi gases is of broad interest, as these systems exhibit universal behavior, where the properties are independent of the details of the microscopic interactions. These gases provide models for testing nonperturbative many-body theories in a variety of fields from neutron stars and nuclear matter to quark-gluon plasmas and high-temperature superconductors. We have observed sound wave propagation throughout the crossover region, by magnetically tuning from a weakly-interacting Fermi gas through the resonant Fermi superfluid regime to a Bose condensate of dimer molecules. The measured sound velocities test the zero-temperature equation of state and confirm the universal hypothesis. We also explore finite-temperature thermodynamics in the universal regime, by measuring the dependence of the entropy on the total energy. These measurements determine the critical temperature for the superfluid transition without invoking any specific theoretical model. [Preview Abstract] |
Friday, June 8, 2007 2:06PM - 2:42PM |
Q1.00002: Universality and novel phases in the BCS-BEC crossover Invited Speaker: We discuss the BCS-BEC crossover in a degenerate Fermi gas near a Feshbach resonance. The origin and experimental verification of universal thermodynamic and dynamic properties at resonance is discussed. In the spin imbalanced situation, novel phases appear like a `magnetized' superfluid or a (FFLO) phase with nonzero momentum Cooper pairs. Their qualitative properties and the associated experimental signatures are outlined. [Preview Abstract] |
Friday, June 8, 2007 2:42PM - 3:18PM |
Q1.00003: Pairing of Fermions with Unequal Spin Populations Invited Speaker: Ultracold atomic fermions hold great promise for simulating important, and in some cases, unsolved models of condensed matter physics. In addition to being clean and well-characterized, the physical parameters of ultracold atomic gases are readily tunable. Notably, the tunability of interactions via a Feshbach resonance has enabled the realization of the BEC-BCS crossover in a two component Fermi gas. The spin polarization of an atomic gas may also be varied by creating a population imbalance of the two components.\footnote{M. W. Zwierlein \emph{et al.}, \emph {Science} \textbf{311}, 492 (2006).}$^,$\footnote{G. B. Partridge \emph{et al.}, \emph{Science} \textbf{311}, 503 (2006).} I will discuss our \emph{in-situ} measurements of the real-space density distributions of polarized mixtures of $^6 $Li atoms.$^{3,}$\footnote{G. B. Partridge \emph{et al.}, \emph {Phys. Rev. Lett.} \textbf{97}, 190407 (2006).} We identify three distinct phases: two contain an unpolarized, fully paired core, while the third is the polarized normal phase. At the lowest temperatures, the gas phase separates into an unpolarized superfluid core with the unpaired atoms residing in a fully polarized normal shell. In this case, the boundary between the superfluid and normal phases is sharp, consistent with a first-order phase transition, and the core is distorted by what is believed to be surface tension between the superfluid and normal components. At slightly higher temperature, the transition between the phases is continuous, resulting in a partially polarized shell structure, without distortion. These observations are consistent with a tricritical point in the phase diagram. [Preview Abstract] |
Friday, June 8, 2007 3:18PM - 3:54PM |
Q1.00004: An atomic Fermi gas near a p-wave Feshbach resonance Invited Speaker: Atomic scattering resonances, called Feshbach resonances, have been used to create molecular Bose-Einstein condensates and Fermi superfluids.~ Past work has focused on s-wave, or non-rotating, pairs created from two fermionic atoms. I will report on investigations of pair creation in an ultracold Fermi gas of potassium-40 atoms near a p-wave Feshbach resonance. [Preview Abstract] |
Friday, June 8, 2007 3:54PM - 4:06PM |
Q1.00005: Pairing of Strongly Interacting Fermions without Superfluidity Christian Schunck, Yong-Il Shin, Andre Schirotzek, Martin Zwierlein, Wolfgang Ketterle We use radio-frequency spectroscopy to study pairing in the normal and superfluid phases of a strongly interacting Fermi gas with imbalanced spin populations. At high spin imbalances the system cannot become superfluid even at zero temperature. In this normal phase full pairing of the minority atoms is observed. This 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. [Preview Abstract] |
Friday, June 8, 2007 4:06PM - 4:18PM |
Q1.00006: Observation of Phase Separation in a Strongly-Interacting Imbalanced Fermi Gas Andre Schirotzek, Yong-Il Shin, Martin Zwierlein, Christian Schunck, Wolfgang Ketterle We have observed phase separation between the superfluid and the normal component in a strongly interacting Fermi gas with imbalanced spin populations. The in situ distribution of the density difference between two trapped spin components is obtained using phase-contrast imaging and 3D image reconstruction. A shell structure is clearly identified where the superfluid region of equal densities is surrounded by a normal gas of unequal densities. The phase transition induces a dramatic change in the density profiles as excess fermions are expelled from the superfluid. [Preview Abstract] |
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