Browsing by Author "Gong, Ming"
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Item Dzyaloshinskii-Moriya Interaction and Spiral Order in Spin-Orbit Coupled Optical Lattices(Nature Publishing Group, 2015-05-27) Gong, Ming; Qian, Yinyin; Yan, Mi; Scarola, V. W.; Zhang, Chuanwei; H-3571-2011 (Zhang, C); Zhang, ChuanweiWe show that the recent experimental realization of spin-orbit coupling in ultracold atomic gases can be used to study different types of spin spiral order and resulting multiferroic effects. Spin-orbit coupling in optical lattices can give rise to the Dzyaloshinskii-Moriya (DM) spin interaction which is essential for spin spiral order. By taking into account spin-orbit coupling and an external Zeeman field, we derive an effective spin model in the Mott insulator regime at half filling and demonstrate that the DM interaction in optical lattices can be made extremely strong with realistic experimental parameters. The rich finite temperature phase diagrams of the effective spin models for fermions and bosons are obtained via classical Monte Carlo simulations.Item FFLO Superfluids in 2d Spin-Orbit Coupled Fermi Gases(2014-10-07) Zheng, Zhen; Gong, Ming; Zhang, Yichao; Zou, Xubo; Zhang, Chuanwei; Guo, Guangcan; Zhang, ChuanweiWe show that the combination of spin-orbit coupling and in-plane Zeeman field in a two-dimensional degenerate Fermi gas can lead to a larger parameter region for Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) phases than that using spin-imbalanced Fermi gases. The resulting FFLO superfluids are also more stable due to the enhanced energy difference between FFLO and conventional Bardeen-Cooper-Schrieffer (BCS) excited states. We clarify the crucial role of the symmetry of Fermi surface on the formation of finite momentum pairing. The phase diagram for FFLO superfluids is obtained in the BCS-BEC crossover region and possible experimental observations of FFLO phases are discussed.Item Majorana Fermions in Quasi-One-Dimensional and Higher-Dimensional Ultracold Optical Lattices(2015-08-14) Qu, Chunlei; Gong, Ming; Xu, Yong; Tewari, Sumanta; Zhang, Chuanwei; Qu, Chunlei; Zhang, ChuanweiWe study Majorana fermions (MFs) in quasi-one dimensional (quasi-1D) and higher-dimensional fermionic optical lattices with a strictly 1D spin-orbit coupling, which has already been realized in cold atom experiments. We show that when the superfluid order parameters are homogeneous and are enforced to be identical along different chains, there are multiple MFs at each end with or without an experimentally tunable in-plane Zeeman field V{y}. For V{y} = 0 the multiple MFs are topologically protected by a chiral symmetry; however, for V{y} ≠ 0 the existence of multiple MFs is related to the peculiar spectrum properties of the system despite the broken chiral symmetry. In the generalization to higher dimensions, the multiple MFs form a zero-energy flat band. Furthermore, when the superfluid order parameters are solved self-consistently, the multiple MFs are usually destroyed because of the inhomogeneous order parameters of either Bardeen-Cooper-Schrieffer (V{y} = 0) type or Fulde-Ferrell (V{y} ≠ 0). Our results are useful to guide the experimentalists on searching for MFs in ultracold spin-orbit coupled fermionic superfluids.Item Spin-Orbit-Driven Transitions between Mott Insulators and Finite-Momentum Superfluids of Bosons in Optical Lattices(Amer Physical Soc, 2018-11-05) Yan, Mi; Qian, Yinyin; Hui, Hoi-Yin; Gong, Ming; Zhang, Chuanwei; Scarola, V. W.; 0000 0000 3722 2361 (Zhang, C); 4042455 (Zhang, C); Qian, Yinyin; Gong, Ming; Zhang, ChuanweiSynthetic spin-orbit coupling in ultracold atomic gases can be taken to extremes rarely found in solids. We study a two-dimensional Hubbard model of bosons in an optical lattice in the presence of spin-orbit coupling strong enough to drive direct transitions from Mott insulators to superfluids. Here we find phase-modulated superfluids with finite momentum that are generated entirely by spin-orbit coupling. We investigate the rich phase patterns of the superfluids, which may be directly probed using time-of-flight imaging of the spin-dependent momentum distribution.Item Statistical Properties of Exciton Fine Structure Splitting and Polarization Angles in Quantum Dot Ensembles(American Physical Society, 2014-05-20) Gong, Ming; Hofer, B.; Zallo, E.; Trotta, R.; Luo, J. -W; Schmidt, O. G.; Zhang, Chuanwei; Zhang, ChuanweiWe develop an effective model to describe the statistical properties of exciton fine structure splitting (FSS) and polarization angle in quantum dot ensembles (QDEs) using only a few symmetry-related parameters. The connection between the effective model and the random matrix theory is established. Such effective model is verified both theoretically and experimentally using several rather different types of QDEs, each of which contains hundreds to thousands of QDs. The model naturally addresses three fundamental issues regarding the FSS and polarization angels of QDEs, which are frequently encountered in both theories and experiments. The answers to these fundamental questions yield an approach to characterize the optical properties of QDEs. Potential applications of the effective model are also discussed.Item Tunable Spin-Orbit Coupling via Strong Driving in Ultracold-Atom Systems(American Physical Society, 2015-03-24) Jim©nez-Garc©a, K.; Leblanc, L. J.; Williams, R. A.; Beeler, M. C.; Qu, Chunlei; Gong, Ming; Zhang, Chuanwei.; Spielman, I. B.; Jim©nez-Garc©a, K.; Leblanc, L. J.; Williams, R. A.; Beeler, M. C.; Qu, Chunlei; Gong, Ming; Zhang, Chuanwei.; Spielman, I. B.Spin-orbit coupling is an essential ingredient in topological materials, conventional and quantum-gas-based alike. Engineered spin-orbit coupling in ultracold-atom systems - unique in their experimental control and measurement opportunities - provides a major opportunity to investigate and understand topological phenomena. Here we experimentally demonstrate and theoretically analyze a technique for controlling spin-orbit coupling in a two-component Bose-Einstein condensate using amplitude-modulated Raman coupling.