科研之友
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摘要
Recent experiments on the shear viscosity eta in a unitary Fermi gas fail to see the theoretically predicted upturn in eta at the lower T. In this Letter, we compute eta in a fashion which is demonstrably consistent with conservation laws and, in the process, provide an understanding of recent experiments. We show that this disagreement with prior theories cannot be readily attributed to the trap, since (via edge effects) trap-averaged viscosities will be larger than their homogeneous counterparts. The small values of eta we find can be simply understood; they reflect the fact that the Goldstone bosons (phonons) do not couple to transverse probes such as eta, and fermionic excitations, which determine the viscosity, are necessarily absent in the ground state.
- 出版日期2011-7-6
- 单位Los Alamos
