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arXiv 0901.2576cond-mat.supr-concond-mat.str-el
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二维费米子超流体、配对不稳定性和无时间反演对称性的涡旋液体

Two-dimensional fermionic superfluids, pairing instability and vortex liquids in the absence of time reversal symmetry

Predrag Nikolic

摘要:

我们考虑一个一般的二维系统的费米子粒子有吸引力的相互作用,没有无序。如果不存在时间反演对称性,除了零温超流之外,还可能得到不可压缩的绝缘态。通过对未成对费米子量子霍尔态库珀对不稳定性的微扰分析,发现在II型系统中超流-绝缘体相变是二级的。我们得到了作为化学势(密度)和温度的函数的配对相图。然而,更仔细的分析表明,配对量子相变总是抢占了另一个过渡到一个强关联的正常状态,保留库珀配对,不能顺利地连接到量子霍尔态的未配对费米子。这样一个正常的阶段可以定性地看作是一个液体的旋涡,虽然它可能获得传统的破缺对称性。即使它不能在有限的温度下生存,它的影响也会通过交叉温标以下的强烈量子涨落而被感受到。这些结论直接适用于接近么正性的费米子超冷原子系统,但也可能与其他强关联超流体的性质有关,包括高温超导体。

英文摘要:

We consider a generic two-dimensional system of fermionic particles with attractive interactions and no disorder. If time-reversal symmetry is absent, it is possible to obtain incompressible insulating states in addition to the superfluid at zero temperature. The superfluid-insulator phase transition is found to be second order in type-II systems using a perturbative analysis of Cooper pairing instability in quantum Hall states of unpaired fermions. We obtain the pairing phase diagram as a function of chemical potential (density) and temperature. However, a more careful analysis presented here reveals that the pairing quantum phase transition is always preempted by another transition into a strongly correlated normal state which retains Cooper pairing and cannot be smoothly connected to the quantum Hall state of unpaired fermions. Such a normal phase can be qualitatively viewed as a liquid of vortices, although it may acquire conventional broken symmetries. Even if it did not survive at finite temperatures its influence would be felt through strong quantum fluctuations below a crossover temperature scale. These conclusions directly apply to fermionic ultra-cold atom systems near unitarity, but are likely relevant for the properties of other strongly correlated superfluids as well, including high temperature superconductors.

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