Fluctuation effects in rotating Bose-Einstein condensates with broken SU(2) and U(1) x U(1) symmetries in the presence of intercomponent density-density interactions
Fluctuation effects in rotating Bose-Einstein condensates with broken SU(2) and U(1) x U(1) symmetries in the presence of intercomponent density-density interactions
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DOI：
10.1103/physreva.91.013605
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发表时间：
2015-01-06
影响因子：
2.9
通讯作者：
Sudbo, Asle
中科院分区：
文献类型：
--
作者：
Galteland, Peder Notto;Babaev, Egor;Sudbo, Asle
旋转单组分超流体的热涨落和熔化转变已经得到了深入的研究和理解。相比之下，具有密度-密度相互作用的双组分超流体的涡旋基态具有更丰富的多样性，其涡旋态的热效应却很少被研究。本文研究了具有U（1）x U（1）对称性破缺和组分间密度-密度相互作用的超流体中涡旋物质的热效应，以及通过调节散射长度从[U（1）x U（1）]对称性得到更大SU（2）对称性破缺的情况。在前一种情况下，我们发现，除了一级熔化转变之外，该系统还表现出正方形和六边形晶格之间的热驱动相变。然而，我们的主要结果涉及的情况下，凝聚表现出SU（2）对称性，涡是不是拓扑。在有限的温度下，该系统表现出的效果，没有在单组分系统的对应。也就是说，它有一个状态，热平均量显示没有规则的涡格，但系统保持超流相干沿着旋转轴。在这种状态下，热波动导致不同（近）简并涡旋状态之间的转变，而不经历熔化转变。我们的结果适用于多组分玻色-爱因斯坦凝聚，我们建议如何检测这些不寻常的影响实验在这样的系统。
Thermal fluctuations and melting transitions for rotating single-component superfluids have been intensively studied and are well understood. In contrast, the thermal effects on vortex states for two-component superfluids with density-density interaction, which have a much richer variety of vortex ground states, have been much less studied. Here, we investigate the thermal effects on vortex matter in superfluids with U(1) x U(1) broken symmetries and intercomponent density-density interactions, as well as the case with a larger SU(2) broken symmetry obtainable from the [U(1) x U(1)]-symmetric case by tuning scattering lengths. In the former case we find that, in addition to first-order melting transitions, the system exhibits thermally driven phase transitions between square and hexagonal lattices. Our main result, however, concerns the case where the condensate exhibits SU(2) symmetry, and where vortices are not topological. At finite temperature, the system exhibits effects which do not have a counterpart in single-component systems. Namely, it has a state where thermally averaged quantities show no regular vortex lattice, yet the system retains superfluid coherence along the axis of rotation. In such a state, the thermal fluctuations result in transitions between different (nearly) degenerate vortex states without undergoing a melting transition. Our results apply to multicomponent Bose-Einstein condensates, and we suggest how to detect some of these unusual effects experimentally in such systems.