Quantum phase transition to unconventional multi-orbital superfluidity in optical lattices
Quantum phase transition to unconventional multi-orbital superfluidity in optical lattices
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DOI：
10.1038/nphys2128
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发表时间：
2012-01-01
期刊：
影响因子：
19.6
通讯作者：
Sengstock, Klaus
中科院分区：
文献类型：
--
作者：
Soltan-Panahi, Parvis;Luehmann, Dirk-Soeren;Sengstock, Klaus
轨道物理在复杂凝聚态系统中的大量重要现象中发挥着重要作用，包括高温超导性和非常规磁性。相比之下，超流体中的现象，特别是超冷量子气体中的现象，通常可以用最低轨道和真实的序参量来描述（1）。在这里，我们报告的观察，一个多轨道的超流相与一个复杂的序参数在二进制自旋混合物。在这种非常规的超流体中，复序参量的局部相角在相邻的晶格位置之间连续扭曲。这种扭曲的超流量子相的性质是实验中使用的六方光学晶格的石墨烯样能带结构所青睐的p轨道贡献的相互作用诱导的混合物。我们观察到一个二阶量子相变之间的正常超流和扭曲的超流相，这是伴随着在动量空间中的对称性破缺。实验结果与计算的相图一致，并从根本上揭示了量子气体混合物中轨道超流性的新方面。我们的研究可能会弥补传统超流现象与复杂轨道物理现象之间的差距。
Orbital physics plays a significant role for a vast number of important phenomena in complex condensed-matter systems, including high-temperature superconductivity and unconventional magnetism. In contrast, phenomena in superfluids-in particular in ultracold quantum gases-are typically well described by the lowest orbital and a real order parameter(1). Here, we report on the observation of a multi-orbital superfluid phase with a complex order parameter in binary spin mixtures. In this unconventional superfluid, the local phase angle of the complex order parameter is continuously twisted between neighbouring lattice sites. The nature of this twisted superfluid quantum phase is an interaction-induced admixture of the p-orbital contributions favoured by the graphene-like band structure of the hexagonal optical lattice used in the experiment. We observe a second-order quantum phase transition between the normal superfluid and the twisted superfluid phase, which is accompanied by a symmetry breaking in momentum space. The experimental results are consistent with calculated phase diagrams and reveal fundamentally new aspects of orbital superfluidity in quantum gas mixtures. Our studies might bridge the gap between conventional superfluidity and complex phenomena of orbital physics.