Exotic Ising dynamics in a Bose-Hubbard model

We explore the dynamical properties of a one-dimensional Bose-Hubbard model, where two bosonic species interact via Feshbach resonance. We focus on the region in the phase diagram which is described by an effective, low-energy ferromagnetic Ising model in both transverse and longitudinal fields. In this regime, we numerically calculate the dynamical structure factor of the Bose-Hubbard model using the time-evolving block decimation method. In the ferromagnetic phase, we observe both the continuum of excitations and the bound states in the presence of a longitudinal field. Near the Ising critical point, we observe the celebrated E8 mass spectrum in the excited states. We also point out possible measurements which could be used to detect these excitations in an optical lattice experiment.Comment: 5 pages, 3 figures, as publishe

The infosource scale: a measure to assess the importance of external tourism information sources

Information sources have long been considered an important variable in understanding consumer purchasing behaviors. Although research on information sources has been performed in a wide range of social disciplines, this variable has never been operationalized in a services marketing context. In this paper we develop a scale that measures the importance of information sources to the selection of tourism services. Insights from an empirical study of 350 tourists indicates that this multi-dimensional scale incorporates five types of information sources: 1) media, 2) institutional brochures, 3) commercial brochures, 4) travel agents, and 5) internet. Discussion centers on implications of this scale to theory and managerial development of tourism and services strategies. Directions for future research are also presented.Tourism, Information Sources, Services Marketing, Communication

Competition between supersolid phases and magnetisation plateaux in the frustrated easy-axis antiferromagnet on a triangular lattice

The majority of magnetic materials possess some degree of magnetic anisotropy, either at the level of a single ion, or in the exchange interactions between different magnetic ions. Where these exchange interactions are also frustrated, the competition between them and anisotropy can stabilize a wide variety of new phases in applied magnetic field. Motivated by the hexagonal delafossite 2H-AgNiO 2, we study the Heisenberg antiferromagnet on a layered triangular lattice with competing first- and second-neighbour interactions and single-ion easy-axis anisotropy. Using a combination of classical Monte Carlo simulation, mean-field analysis, and Landau theory, we establish the magnetic phase diagram of this model as a function of temperature and magnetic field for a fixed ratio of exchange interactions, but with values of easy-axis anisotropy D extending from the Heisenberg (D =0) to the Ising (D=&#8734) limits. We uncover a rich variety of different magnetic phases. These include several phases which are magnetic supersolids (in the sense of Matsuda and Tstuneto or Liu and Fisher), one of which may already have been observed in AgNiO 2. We explore how this particular supersolid arises through the closing of a gap in the spin-wave spectrum, and how it competes with rival collinear phases as the easy-axis anisotropy is increased. The finite temperature properties of this phase are found to be different from those of any previously studied magnetic supersolid.Comment: 25 pages; 29 figures; minor revisions; accepted for publication in Phys. Rev.

Supersolid phases in a realistic three-dimensional spin model

Supersolid phases, in which a superfluid component coexists with conventional crystalline long range order, have recently attracted a great deal of attention in the context of both solid helium and quantum spin systems. Motivated by recent experiments on 2H-AgNiO$_2$, we study the magnetic phase diagram of a realistic three-dimensional spin model with single-ion anisotropy and competing interactions on a layered triangular lattice, using classical Monte Carlo simulation techniques, complemented by spin-wave calculations. For parameters relevant to experiment, we find a cascade of different phases as a function of magnetic field, including three phases which are supersolids in the sense of Liu and Fisher. One of these phases is continuously connected with the collinear ground state of AgNiO$_2$, and is accessible at relatively low values of magnetic field. The nature of this low-field transition, and the possibility of observing this new supersolid phase in AgNiO$_2$, are discussed.Comment: 4+\epsilon pages, 5 eps figures; minor revisions; accepted for publication in Phys. Rev. Let

From fractionally charged solitons to Majorana bound states in a one-dimensional interacting model

We consider one-dimensional topological insulators hosting fractionally charged midgap states in the presence and absence of induced superconductivity pairing. Under the protection of a discrete symmetry, relating positive and negative energy states, the solitonic midgap states remain pinned at zero energy when superconducting correlations are induced by proximity effect. When the superconducting pairing dominates the initial insulating gap, Majorana fermion phases develop for a class of insulators. As a concrete example, we study the Creutz model with induced s-wave superconductivity and repulsive Hubbard-type interactions. For a finite wire, without interactions, the solitonic modes originating from the nonsuperconducting model survive at zero energy, revealing a fourfold-degenerate ground state. However, interactions break the aforementioned discrete symmetry and completely remove this degeneracy, thereby producing a unique ground state which ischaracterized by a topological bulk invariant with respect to the product of fermion parity and bond inversion. In contrast, the Majorana edge modes are globally robust to interactions. Moreover, the parameter range for which a topological Majorana phase is stabilized expands when increasing the repulsive Hubbard interaction. The topological phase diagram of the interacting model is obtained using a combination of mean-field theory and density matrix renormalization group techniques.Comment: 20 pages, 20 figure

Real-time dynamics in the one-dimensional Hubbard model

We consider single-particle properties in the one-dimensional repulsive Hubbard model at commensurate fillings in the metallic phase. We determine the real-time evolution of the retarded Green's function by matrix-product state methods. We find that at sufficiently late times the numerical results are in good agreement with predictions of nonlinear Luttinger liquid theory. We argue that combining the two methods provides a way of determining the single-particle spectral function with very high frequency resolution.Comment: 10 pages, 6 figures. Minor edits from v1. Version as publishe

Satisfacción con la atención de enfermería en los consumidores de drogas: evolución de una escala

Objectives: To identify the degree of satisfaction with nursing care, the significant variables and contribute to the evolution of the scale.Methods: Descriptive, correlational, cross study, with 180 drug users. Data collected using the scale called “Satisfaction of users with the Nursing Health Center26”, between February and December 2012 in three treatment units in the region of Lisbon and Vale do Tejo, Portugal. Results: Users indicated 83.3% satisfaction. The dimension “Information individualization” was the most marked (98.5%). The more stability in the programs, abstinence from stimulants and benzodiazepines and more nursing interventions, the greater the satisfaction. Better working conditions, specializing in mental health, younger ages and less experience of nurses also contributed to satisfaction. Four items of the scale were extracted, assuming new SUCECS22 designation. Conclusions: Satisfaction was high, influenced by structural variables of users, nurses and working conditions. The scale has proved suitable for assessment in this population.info:eu-repo/semantics/publishedVersio