COMP Center of Excellence, Department of Applied Physics, Aalto University, Fi-00076, Aalto, Finland.
Rep Prog Phys. 2018 Apr;81(4):046401. doi: 10.1088/1361-6633/aaa4ad. Epub 2018 Jan 2.
We review the concepts and the present state of theoretical studies of spin-imbalanced superfluidity, in particular the elusive Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) state, in the context of ultracold quantum gases. The comprehensive presentation of the theoretical basis for the FFLO state that we provide is useful also for research on the interplay between magnetism and superconductivity in other physical systems. We focus on settings that have been predicted to be favourable for the FFLO state, such as optical lattices in various dimensions and spin-orbit coupled systems. These are also the most likely systems for near-future experimental observation of the FFLO state. Theoretical bounds, such as Bloch's and Luttinger's theorems, and experimentally important limitations, such as finite-size effects and trapping potentials, are considered. In addition, we provide a comprehensive review of the various ideas presented for the observation of the FFLO state. We conclude our review with an analysis of the open questions related to the FFLO state, such as its stability, superfluid density, collective modes and extending the FFLO superfluid concept to new types of lattice systems.
我们在超冷量子气体的背景下，回顾了自旋不平衡超流的理论研究的概念和现状，特别是难以捉摸的富勒-费雷尔-拉金-奥夫钦尼科夫（FFLO）态。我们提供的 FFLO 态的理论基础的全面介绍，对于研究其他物理系统中的磁学和超导相互作用也很有用。我们专注于预测有利于 FFLO 态的环境，例如各种维度的光晶格和自旋轨道耦合系统。这些也是最有可能在近期进行 FFLO 态实验观测的系统。我们考虑了理论限制，如布洛赫定理和吕特廷格定理，以及实验上重要的限制，如有限大小效应和俘获势。此外，我们还对为观察 FFLO 态而提出的各种想法进行了全面的综述。我们的综述以分析与 FFLO 态相关的未解决问题结束，例如其稳定性、超流密度、集体模式以及将 FFLO 超流概念扩展到新型晶格系统。
