G. M. Bruun

Viscous relaxation and collective oscillations in a trapped Fermi gas near the unitarity limit

The viscous relaxation time of a trapped two-component gas of fermions in its normal phase is calculated as a function of temperature and scattering length, with the collision probability being determined by an energy-dependent

Shear viscosity and damping for a fermi gas in the unitarity limit

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Viscosity and thermal relaxation for a resonantly interacting Fermi gas

-wave cross section. The result is used for calculating the temperature dependence of the frequency and damping of collective modes studied in recent experiments, starting from the kinetic equation for the fermion distribution function with mean-field effects included in the streaming terms.

Effective theory of Feshbach resonances and many-body properties of Fermi gases

The shear viscosity of a two-component Fermi gas in the normal phase is calculated as a function of temperature in the unitarity limit, taking into account strong-coupling effects that give rise to a pseudogap in the spectral density for single-particle excitations. The results indicate that recent measurements of the damping of collective modes in trapped atomic clouds can be understood in terms of hydrodynamics, with a decay rate given by the viscosity integrated over an effective volume of the cloud.

Short-range correlations and entropy in ultracold-atom Fermi gases

The viscous and thermal relaxation rates of an interacting fermion gas are calculated as functions of temperature and scattering length, using a many-body scattering matrix which incorporates medium effects due to Fermi blocking of intermediate states. These effects are demonstrated to be large close to the transition temperature T{sub c} to the superfluid state. For a homogeneous gas in the unitarity limit, the relaxation rates are increased by nearly an order of magnitude compared to their value obtained in the absence of medium effects due to the Cooper instability at T{sub c}. For trapped gases the corresponding ratio is found to be about three due to the averaging over the inhomogeneous density distribution. The effect of superfluidity below T{sub c} is considered to leading order in the ratio between the energy gap and the transition temperature.

Microscopic structure of a vortex line in a dilute superfluid Fermi gas

For calculating low-energy properties of a dilute gas of atoms interacting via a Feshbach resonance, we develop an effective theory in which the parameters that enter are an atom-molecule coupling strength and the magnetic moment of the molecular resonance. We demonstrate that, for resonances in the fermionic systems 6Li and 40K that are under experimental investigation, the coupling is so strong that many-body effects are appreciable even when the resonance lies at an energy large compared with the Fermi energy. We calculate a number of many-body effects, including the effective mass and the lifetime of atomic quasiparticles in the gas.

Twin peaks in rf spectra of Fermi gases at unitarity

We relate short-range correlations in ultracold atomic Fermi gases to the entropy of the system over the entire temperature,

Bragg Spectroscopy of Cold Atomic Fermi Gases

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Detection of BCS pairing in neutral fermi fluids via stokes scattering: the Hebel-Slichter effect.

, vs. coupling strength,

Pairing fluctuations in trapped Fermi gases

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