Bulletin of the American Physical Society
40th Annual Meeting of the APS Division of Atomic, Molecular and Optical Physics
Volume 54, Number 7
Tuesday–Saturday, May 19–23, 2009; Charlottesville, Virginia
Session R1: Focus Session: Fermi Gases |
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Chair: Randy Hulet, Rice University Room: Chemistry Building 402 |
Friday, May 22, 2009 10:30AM - 11:00AM |
R1.00001: Theory of BCS-BEC Crossover in Ultracold Fermi Gases: Insights into Thermodynamical and Spectroscopic Experiments Invited Speaker: In this talk we summarize our theoretical understanding of the atomic Fermi superfluids with an emphasis on understanding current experiments. We compare and contrast different theoretical approaches for dealing with finite temperature, and discuss their respective implications for these trapped gases. Armed with a basic picture of the thermodynamics we turn to a variety of different measurements based on radio frequency spectroscopy, including both momentum integrated and momentum resolved experiments. As recently reviewed in arXiv 0810.1940 and 0810.1938, we show how a broad range of experimental phenomena can be accomodated within our natural extension of the BCS-Leggett ground state to finite temperature, and briefly touch on the applicability of BCS-BEC crossover theory to the high temperature superconductors. Co-authors: Qijin Chen, Yan He and Chih-Chun Chien [Preview Abstract] |
Friday, May 22, 2009 11:00AM - 11:30AM |
R1.00002: Experiments with Interacting Fermi Gases Invited Speaker: An optically-trapped mixture of spin 1/2-up and spin 1/2-down $^6$Li atoms provides a paradigm for exploring interacting Fermi systems in nature. This ultracold atomic gas offers unprecedented opportunities to test theoretical techniques that cross interdisciplinary boundaries. A bias magnetic field is used to tune the gas near a Feshbach resonance, enabling studies from the weakly interacting regime to the most strongly interacting nonrelativistic system known. In the weakly interacting regime, the gas exhibits nearly undamped spin waves. In the strongly interacting regime, it exhibits a high temperature superfluid transition and extremely low viscosity hydrodynamics in the normal fluid. The strongly interacting regime is of great interest in the quark-gluon plasma and string theory communities, where it has been conjectured that the ratio of the shear viscosity to the entropy density has a universal lower bound, which defines a perfect fluid. I will describe our all-optical cooling methods and our studies of the thermodynamic and hydrodynamic properties of the $^6$Li cloud, as well as our discovery of a new mechanism for creating spin waves in this system. [Preview Abstract] |
Friday, May 22, 2009 11:30AM - 11:42AM |
R1.00003: Zero Sound in Fermi Dipolar Condensates Shai Ronen, John Bohn We study zero sound in degenerate dipolar Fermi in the normal phase. Zero sound is a coherent superposition of particle-hole excitations near the Fermi surface. This phenomena is of particular interest in dipolar gases due to the long range and non-isotropic interactions. In fact, these interactions already deform the equilibrium Fermi surface so that it is no longer spherical. We find that zero sound can propagate parallel to the polarization direction of the gas but is damped in the transverse direction. [Preview Abstract] |
Friday, May 22, 2009 11:42AM - 11:54AM |
R1.00004: Biaxial nematic phases in ultracold dipolar Fermi gases Benjamin Fregoso, Kai Sun, Eduardo Fradkin, Benjamin Lev Ultracold dipolar Fermi gases represent a relatively unexplored, strongly correlated system arising from long-range and anisotropic interactions. We demonstrate the possibility of a spontaneous symmetry breaking biaxial phase in these systems, which may be realized in, e.g., gases of ultracold polar molecules or strongly magnetic atoms. This biaxial nematic phase is manifest in a distortion of the Fermi surface perpendicular to the axis of polarization, and is a phase distinct from the previously discussed uniaxial distortion caused by any non-zero external polarizing field. We describe these dipolar interaction induced phases using Landau Fermi liquid theory and point to possible light scattering measurements that could detect these strong dipolar effects in degenerate Fermi gases. [Preview Abstract] |
Friday, May 22, 2009 11:54AM - 12:06PM |
R1.00005: Superfluid density profile in a trapped Fermi gas Nicolai Nygaard, Hui Hu, Xia-Ji Liu We present a microscopic calculation of the local superfluid density for a Fermi gas with a spatially varying density profile. By imposing an infinitesimal twist on the phase of the order parameter and calculating the resulting strain energy perturbatively, we find the helicity modulus, which is directly tied to the density of the superfluid component. The superfluid density determines the moment of inertia and in a two-fluid description of the hydrodynamics it is fundamental in a calculation of the collective mode frequencies. [Preview Abstract] |
Friday, May 22, 2009 12:06PM - 12:18PM |
R1.00006: Trapped fermion mixtures with unequal masses: a Bogoliubov-de Gennes approach Menderes Iskin, Carl Williams We use the Bogoliubov-de Gennes formalism to analyze the ground state phases of harmonically trapped two-species fermion mixtures with unequal masses. In the weakly attracting limit and around unitarity, we find that the superfluid order parameter is spatially modulated around the trap center, and that its global maximum occurs at a finite distance away from the trap center where the mixture is locally unpolarized. As the attraction strength increases towards the molecular limit, the spatial modulations gradually disappear while the Bardeen-Cooper-Schrieffer (BCS) type nonmodulated superfluid region expands until the entire mixture becomes locally unpolarized. [Preview Abstract] |
Friday, May 22, 2009 12:18PM - 12:30PM |
R1.00007: A ``Dilution Refrigerator'' Using Spin-Polarized Fermions Sourish Basu, Erich J. Mueller We present an analogy between a population imbalanced two component Fermi gas on the BEC side of a Feshbach resonance and a $^3$He-$^4$He mixture. The bosonic pairs are analogous to $^4$He and the fermionic unpaired atoms to $^3$He. These systems have topologically indistinguishable phase diagrams: at low temperatures the system phase separates into a fermion rich and a fermion poor region. As in standard cryogenic setups, one can in principle create a refrigerator which cools based upon the fact that there is a latent heat associated with pulling particles from the fermion rich region into the fermion poor one. We explore this idea, calculating the entropy of mixing, and suggesting cold atom geometries which mimic the anatomy of a standard $^3$He-$^4$He dilution refrigerator. [Preview Abstract] |
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