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arXiv 0812.5028cond-mat.quant-gascond-mat.supr-con
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存在费什巴赫共振的两组分费米子系统破缺对态的稳定性

Stability of the Breached Pair State for a Two-species Fermionic System in the Presence of Feshbach Resonance

Raka Dasgupta

摘要:

我们研究了在费什巴赫共振存在下,两种物质系统中费米子与费米子面失配的配对现象,即配对的费米子结合形成玻色子分子.我们观察到Feshbach参数控制着带隙BCS超流态的临界温度,同时也决定了无隙破缺对态可能存在的范围。在超流密度为正的条件下,证明了虽然具有两个费米面的破缺对态总是不稳定的,但如果两个对态的化学势符号相反,则它的单个费米面对应态是稳定的.该条件仅在BEC侧的窄区域上满足,其特征在于磁场的上限和下限。我们估计这些限制的混合物的两个超精细态的$^6$锂使用最近的实验数据。

英文摘要:

We investigate the phenomenon of fermionic pairing with mismatched Fermi surfaces in a two-species system in the presence of Feshbach resonance, where the resonantly-paired fermions combine to form bosonic molecules. We observe that the Feshbach parameters control the critical temperature of the gapped BCS superfluid state, and also determine the range over which a gapless breached pair state may exist. Demanding the positivity of the superfluid density, it is shown that although a breached pair state with two Fermi surfaces is always unstable, its single Fermi-surface counterpart can be stable if the chemical potentials of the two pairing species have opposite signs. This condition is satisfied only over a narrow region in the BEC side, characterized by an upper and a lower limit for the magnetic field. We estimate these limits for a mixture of two hyperfine states of $^6$Li using recent experimental data.

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