Bulletin of the American Physical Society
APS March Meeting 2017
Volume 62, Number 4
Monday–Friday, March 13–17, 2017; New Orleans, Louisiana
Session E13: Spin-Orbit Coupled Atomic Gases |
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Sponsoring Units: DAMOP Chair: Vito Scarola, Virginia Tech University Room: 272 |
Tuesday, March 14, 2017 8:00AM - 8:12AM |
E13.00001: Fermions on the Bloch bands of shaken square optical lattice Ahmet Keles, Erhai Zhao, Vincent Liu We study the interplay between multiple Bloch bands and interactions facilitated by a time-periodic drive in a system of ultracold Fermions in two dimensional square optical lattice. The periodic drive is chosen to be in circular orbit and its frequency is tuned to the gap between ground state s-band and two fold degenerate p-bands. Using the numerical Floquet formalism, we obtain the single particle quasi-energy spectrum by including all higher bands. We analytically derive an effective time independent Hamiltonian fully consistent with the numerical Floquet solution by considering the lowest four orbitals and show that s-band mixed with higher bands via shaking displays a set of non-trivial Fermi surfaces. We obtain the effective interactions of the particles in the mixed s-band and show that a simple onsite interaction gives rise to momentum dependent interaction on the Fermi surface. Considering attractive interactions tuned via Feshbach resonance in the weak coupling limit, we obtain the phase diagram and the pairing symmetries as a function of lattice filling. [Preview Abstract] |
Tuesday, March 14, 2017 8:12AM - 8:24AM |
E13.00002: Searching new topological superfluids and phase transitions with spin-orbit coupled fermions in an optical lattice Yu Yixiang, Fadi Sun, Jinwu Ye, Ningfang Song We study the global phase diagram of attractively interacting fermions hopping in a square lattice with any linear combinations of Rashba or Dresselhaus spin-orbit coupling (SOC) in a normal Zeeman field. Here, we focus on half filling case. We find there are 3 phases Band insulator, Superfluid (SF) and Topological SF with C$=$2. The TSF happens in small Zeeman fields and very weak interactions which is the experimentally most easily accessible regimes and has also the smallest heating effects. The transition from the BI to the SF is a first order one due to the multi-minima structure of the energy landscape. There is a topological phase transition from the SF to the TSF at the low critical field h\textunderscore \textbraceleft c1\textbraceright , then another one from the TSF to the BI at the upper critical field h\textunderscore \textbraceleft c2\textbraceright . We derive effective actions to describe the two topological phase transitions, then study the edge modes and the Majorana zero modes inside a vortex core of the C$=$2 TSF near both h\textunderscore \textbraceleft c1\textbraceright and h\textunderscore \textbraceleft c2\textbraceright . We map out the local Berry Curvature distribution near both h\textunderscore \textbraceleft c1\textbraceright and h\textunderscore \textbraceleft c2\textbraceright . We find a topological tri-critical point along h\textunderscore \textbraceleft c1\textbraceright and conjecture that any topological transitions can only be odd order. We also study some bulk-Berry curvature-edge-vortex correspondences. [Preview Abstract] |
Tuesday, March 14, 2017 8:24AM - 8:36AM |
E13.00003: Effect of Zeeman Field and Spin-Orbit Coupling on Fermi Gases in Optical Lattices Haiyang Zhang, Hai-Chao Li, Xiangyu Xiong, Guo-Qin Ge In this paper, we study spin-orbit coupled Fermi gases with Zeeman field in optical lattices using the Bogoliubov-de Gennes equation and mean field theory in the two-channel model. We analyze the results of two and single-channel models for different strengths of atom-molecule couplings, Zeeman field and spin-orbit couplings. We find that in the broad resonance condition or the strength of Zeeman field is strong, the single-channel model can substitute the two-channel model without any lack of accuracy. In contrast, a strong spin-orbit coupling suppresses the effect of a broad resonance and Zeeman field and the two-channel model cannot be substituted in this limit. In the two channel model, we find that there is a peak of molecular fraction with increasing strength of the atom-molecule couplings. Furthermore, it is found that Zeeman field plays a crucial role in polarizing spin of the Fermi atoms while the spin-orbit coupling suppresses the spin polarization of the ultracold Fermi gases. [Preview Abstract] |
Tuesday, March 14, 2017 8:36AM - 8:48AM |
E13.00004: Two-dimensional Fermi gas in spin-dependent magnetic fields Takaaki Anzai, Yusuke Nishida Experimental techniques in ultracold atoms allow us to tune parameters of the system at will. In particular, synthetic magnetic fields have been created by using the atom-light coupling and, therefore, it is interesting to study what kinds of quantum phenomena appear in correlated ultracold atoms subjected to synthetic magnetic fields. In this work, we consider a two-dimensional Fermi gas with two spin states in spin-dependent magnetic fields which are assumed to be antiparallel for different spin states~[1]. By studying the ground-state phase diagram within the mean-field approximation, we find quantum spin Hall and superfluid phases separated by a second-order phase transition. We also show that there are regions where the superfluid gap parameter is proportional to the attractive coupling, which is in marked contrast to the usual exponential dependence. Moreover, we elucidate that the universality class of the phase transition belongs to that of the XY model at special points of the phase boundary, while it belongs to that of a dilute Bose gas anywhere else~[2]. [1] M. C. Beeler et al., Nature \textbf{498}, 201 (2013). [2] T. Anzai and Y. Nishida, in preparation. [Preview Abstract] |
Tuesday, March 14, 2017 8:48AM - 9:00AM |
E13.00005: A Semiclassical Treatment of Spin Currents for Dirac Particles in Rotating Coordinates Elif Yunt, Omer Faruk Dayi Spin currents for Dirac particles in the presence of external electromagnetic fields and global rotation in both two and three dimensions is presented. The particle distributions are derived using the Boltzmann transport equation with collision in the relaxation-time approximation. In the Boltzmann equation, we employ the matrix-valued semiclassical equations of motion established in [1]. Spin currents are calculated within this semiclassical method which is based on the wave packet composed of positive energy solutions of the Dirac equation. The Berry Curvature resulting from this wave packet contributes to the equations of motion. We comment on the pure spin current generation in three dimensions, which is a main focus in the field of spintronics, by calculating the spin current and particle number densities associated with holes (or antiparticles). [1] \"{O}. F. Dayi, E. Kilin\c{c}arslan and E. Yunt, arXiv: 1605.05451 [Preview Abstract] |
Tuesday, March 14, 2017 9:00AM - 9:12AM |
E13.00006: Realization of uniform synthetic magnetic fields by periodically shaking an optical square lattice Fernando Sols, Charles E. Creffield, Gregor Pieplow, Nathan Goldman Shaking a lattice system, by modulating the location of its sites periodically in time, is a powerful method to create effective magnetic fields in engineered quantum systems, such as cold gases trapped in optical lattices. However, such schemes are typically associated with space-dependent effective masses (tunneling amplitudes) and non-uniform flux patterns. In this work [1] we investigate this phenomenon theoretically, by computing the effective Hamiltonians and quasienergy spectra associated with several kinds of lattice-shaking protocols. A detailed comparison with a method based on moving lattices, which are added on top of a main static optical lattice, is provided. This study allows the identification of novel shaking schemes, which simultaneously provide uniform effective mass and magnetic flux, with direct implications for cold-atom experiments and photonics. [1] C. E. Creffield, G. Pieplow, F. Sols, N. Goldman, New J. Phys. 18, 093013 (2016). [Preview Abstract] |
Tuesday, March 14, 2017 9:12AM - 9:24AM |
E13.00007: Creating fractional quantum Hall states with atomic clusters using light-assisted insertion of angular momentum Junyi Zhang, Jerome Beugnon, Sylvain Nascimbene We describe a protocol to prepare clusters of ultracold bosonic atoms in strongly interacting states reminiscent of fractional quantum Hall states. Our scheme consists in injecting a controlled amount of angular momentum to an atomic gas using Raman transitions carrying orbital angular momentum. By injecting one unit of angular momentum per atom, one realizes a single-vortex state, which is well described by mean-field theory for large enough particle numbers. We also present schemes to realize fractional quantum Hall states, namely, the bosonic Laughlin and Moore-Read states. We investigate the requirements for adiabatic nucleation of such topological states, in particular comparing linear Landau-Zener ramps and arbitrary ramps obtained from optimized control methods. We also show that this protocol requires excellent control over the isotropic character of the trapping potential. [Preview Abstract] |
Tuesday, March 14, 2017 9:24AM - 9:36AM |
E13.00008: Stability of Emergent Kinetics in Optical Lattices with Artificial Spin-Orbit Coupling Mengsu Chen, Vito Scarola Artificial spin-orbit coupling in optical lattices can be engineered to tune band structure into extreme regimes where the single-particle band flattens leaving only inter-particle interactions to define many-body states of matter. Lin et al. [Phys. Rev. Lett 112, 110404 (2014)] showed that under such conditions interactions lead to a Wigner crystal of fermionic atoms under approximate conditions: no bandwidth or band mixing. The excitations were shown to possess emergent kinetics with fractionalized charge derived entirely from interactions. In this work we use numerical exact diagonalization to study a more realistic model with non-zero bandwidth and band mixing. We map out the stability phase diagram of the Wigner crystal. We find that emergent properties of the Wigner crystal excitations remain stable for realistic experimental parameters. Our results validate the approximations made by Lin et al. and define parameter regimes where strong interaction effects generate emergent kinetics in optical lattices. [Preview Abstract] |
Tuesday, March 14, 2017 9:36AM - 9:48AM |
E13.00009: Vortex dynamics in Bose-Einstein condensates with laser-induced spin-orbit coupling Kenichi Kasamatsu We study vortex dynamics in trapped two-component Bose-Einstein condensates with a laser-induced spin-orbit coupling using the numerical analysis of the Gross-Pitaevskii equation. The spin-orbit coupling leads to three distinct ground-state phases, which depend on some experimentally controllable parameters. When a vortex is put in one or both of the two-component condensates, the vortex dynamics exhibits very different behaviors in each phase, which can be observed in experiments. These dynamical behaviors can be understood by clarifying the stable vortex structure realized in each phase. [Preview Abstract] |
Tuesday, March 14, 2017 9:48AM - 10:00AM |
E13.00010: Phase transitions and emergent gauge potentials in strongly interacting spin-orbit coupled bosons William Cole, Khan Mahmud, Jay Sau, Ian Spielman We use DMRG to map out the phase diagram of two-component spin-orbit coupled bosons in one spatial dimension with strong interactions. We locate phase transitions varying the Rabi coupling and wavevector of the spin-orbit coupling as well as the interaction strength. We then focus our attention near the hard-core limit, where we argue for a mapping to an effective model where density fluctuations see the spin texture as a gauge field. We discuss the experimental feasibility of observing these phase transitions through direct imaging of spin domains. [Preview Abstract] |
Tuesday, March 14, 2017 10:00AM - 10:12AM |
E13.00011: Global quantum phase diagram of strongly interacting spinor bosons with generic 2 dimensional spin-orbital couplings in a square lattice Fadi Sun, Jinwu Ye, Wu-Ming Liu Recently, there are ground breaking experimental advances in generating 2 dimensional spin-orbit coupling (SOC) for cold atoms in both continuum and optical lattices. One typical experiment set-up is to load spinor bosons at integer fillings in an optical lattice subject to a 2d SOC. In the strong coupling limit, it leads to the Rotated Ferromagnetic Heisenberg model (RFHM) which is a new class of quantum spin models to describe quantum magnetisms in cold atoms or some materials with strong SOC. In a previous work, we investigate various quantum phenomena of the RFHM along a solvable line in the SOC parameter space. In this talk, starting from the results achieved along the solvable line, we study the RFHM in the whole SOC parameter space. Its global phase diagram displays many novel quantum phenomena such as masses generated from ``order from disorder '' mechanism, quantum commensurate (C) and In-commensurate (IC) skyrmion phases, quantum Lifshitz C-IC transitions, spiral phases, metastable states, hysteresis, devil staircases and fractals, etc. Connections to the classical Frenkel-Kontorowa (FK) model are explored. Implications to cold atom systems and so called Kitaev materials with SOC are discussed. Various intriguing perspectives are outlined. [Preview Abstract] |
Tuesday, March 14, 2017 10:12AM - 10:24AM |
E13.00012: Spin-orbit coupled p-orbital bands Yan-Qi Wang We investigate novel phases for a 2D spin-orbit coupled bosonic p-orbital system based on recent experiments. The orbital degree of freedom and spin-orbit coupling are shown to compete and bring about novel phases in the presence of interactions. We develop a self-consistent method for bosons to solve the phase diagram, with the interesting topological features being discussed. [Preview Abstract] |
Tuesday, March 14, 2017 10:24AM - 10:36AM |
E13.00013: Superfluidity in the absence of kinetics in spin-orbit- coupled optical lattices Hoi-Yin Hui, Yongping Zhang, Chuanwei Zhang, Vito Scarola Recent experiments have succeeded in generating effective spin-orbit coupling for ultracold Bosons in optical lattices. These systems offer the intriguing possibility of generating flat bands when a Zeeman field of suitable strength is applied. In this talk I will discuss possible interesting states that could emerge in such flat band systems. In particular, the fate of superfluidity in the absence of kinetics will be investigated by explicitly constructing a tight-binding model, followed by an unbiased numerical treatment. We find that novel superfluid states can arise entirely from interactions operating in quenched kinetic energy bands, thus revealing a distinct and unexpected boson condensation mechanism. [Preview Abstract] |
Tuesday, March 14, 2017 10:36AM - 10:48AM |
E13.00014: Charge and spin correlations in the 2D Hubbard model realized with ultracold atoms Ehsan Khatami, Lawrence W. Cheuk, Matthew A. Nichols, Katherine R. Lawrence, Melih Okan, Hao Zhang, Nandini Trivedi, Thereza Paiva, Marcos Rigol, Martin W. Zwierlein Site-resolved observation of charge and spin correlations in the two-dimensional Fermi-Hubbard model realized with ultracold atoms has recently been accomplished [1]. It has been found that at large doping, nearest-neighbor correlations between singly charged sites are negative, revealing the formation of a correlation hole, the suppressed probability of finding two fermions near each other. Also, as the doping is reduced, the correlations become positive, signaling strong bunching of doublons and holes. Highly-precise results from numerical linked-cluster expansions and quantum Monte Carlo simulations have played an important role in the accurate characterization of the system and the interpretation of the experimental results. Here, we highlight some of the important new numerical results for the spin and charge correlations of the Hubbard model for various interaction strengths and across doping regimes. [1] Cheuk et al., Science 353, 1260 (2016) [Preview Abstract] |
Tuesday, March 14, 2017 10:48AM - 11:00AM |
E13.00015: Quantum phases of the one-dimensional extended Bose-Hubbard model with spin-orbit coupling David Feder, Farokh Mivehvar Quantum phases of the one-dimensional two-component Bose-Hubbard model with local and nearest-neighbor interactions, spin-orbit coupling, and a transverse magnetic field are explored within a zero-temperature mean-field theory. The interplay of kinetic and interaction energies yields Mott insulator, density wave, superfluid, and supersolid phases for either spin component. With nearest-neighbor interactions one obtains states that are supersolid in one spin component but insulating in the other. Spin-orbit and spin-polarizing terms yield a supersolid phase with antiferromagnetic spin order coupled to a density wave. The results indicate that spin-orbit interactions can drive two-component lattice gases into novel quantum phases. [Preview Abstract] |
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