Directly imaging spin polarons in a kinetically frustrated Hubbard system.

The emergence of quasiparticles in quantum many-body systems underlies the rich phenomenology in many strongly interacting materials. In the context of doped Mott insulators, magnetic polarons are quasiparticles that usually arise from an interplay between the kinetic energy of doped charge carriers and superexchange spin interactions1-8. However, in kinetically frustrated lattices, itinerant spin polarons-bound states of a dopant and a spin flip-have been theoretically predicted even in the absence of superexchange coupling9-14. Despite their important role in the theory of kinetic magnetism, a microscopic observation of these polarons is lacking. Here we directly image itinerant spin polarons in a triangular-lattice Hubbard system realized with ultracold atoms, revealing enhanced antiferromagnetic correlations in the local environment of a hole dopant. In contrast, around a charge dopant, we find ferromagnetic correlations, a manifestation of the elusive Nagaoka effect15,16. We study the evolution of these correlations with interactions and doping, and use higher-order correlation functions to further elucidate the relative contributions of superexchange and kinetic mechanisms. The robustness of itinerant spin polarons at high temperature paves the way for exploring potential mechanisms for hole pairing and superconductivity in frustrated systems10,11. Furthermore, our work provides microscopic insights into related phenomena in triangular-lattice moiré materials17-20.

Observation of Nagaoka polarons in a Fermi-Hubbard quantum simulator.

Quantum interference can deeply alter the nature of many-body phases of matter1. In the case of the Hubbard model, Nagaoka proved that introducing a single itinerant charge can transform a paramagnetic insulator into a ferromagnet through path interference2-4. However, a microscopic observation of this kinetic magnetism induced by individually imaged dopants has been so far elusive. Here we demonstrate the emergence of Nagaoka polarons in a Hubbard system realized with strongly interacting fermions in a triangular optical lattice5,6. Using quantum gas microscopy, we image these polarons as extended ferromagnetic bubbles around particle dopants arising from the local interplay of coherent dopant motion and spin exchange. By contrast, kinetic frustration due to the triangular geometry promotes antiferromagnetic polarons around hole dopants7. Our work augurs the exploration of exotic quantum phases driven by charge motion in strongly correlated systems and over sizes that are challenging for numerical simulation8-10.

Superexchange Liquefaction of Strongly Correlated Lattice Dipolar Bosons.

We propose a mechanism for liquid formation in strongly correlated lattice systems. The mechanism is based on an interplay between long-range attraction and superexchange processes. As an example, we study dipolar bosons in one-dimensional optical lattices. We present a perturbative theory and validate it in comparison with full density-matrix renormalization group simulations for the energetic and structural properties of different phases of the system, i.e., self-bound Mott insulator, liquid, and gas. We analyze the nonequilibrium properties and calculate the dynamic structure factor. Its structure differs in compressible and insulating phases. In particular, the low-energy excitations in compressible phases are linear phonons. We extract the speed of sound and analyze its dependence on dipolar interaction and density. We show that it exhibits a nontrivial behavior owing to the breaking of Galilean invariance. We argue that an experimental detection of this previously unknown quantum liquid could provide a fingerprint of the superexchange process and open intriguing possibilities for investigating non-Galilean invariant liquids.

Universal Dimerized Quantum Droplets in a One-Dimensional Lattice.

The ground-state properties of two-component bosonic mixtures in a one-dimensional optical lattice are studied both from few- and many-body perspectives. We rely directly on a microscopic Hamiltonian with attractive intercomponent and repulsive intracomponent interactions to demonstrate the formation of a quantum liquid. We reveal that its formation and stability can be interpreted in terms of finite-range interactions between dimers. We derive an effective model of composite bosons (dimers) which correctly captures both the few- and many-body properties and validate it against exact results obtained by the density matrix renormalization group method for the full Hamiltonian. The threshold for the formation of the liquid coincides with the appearance of a bound state in the dimer-dimer problem and possesses a universality in terms of the two-body parameters of the dimer-dimer interaction, namely, scattering length and effective range. For sufficiently strong effective dimer-dimer repulsion we observe fermionization of the dimers which form an effective Tonks-Girardeau state and identify conditions for the formation of a solitonic solution. Our predictions are relevant to experiments with dipolar atoms and two-component mixtures.

[Teenager counselling in primary care]. / Consejería a adolescentes: descripción epidemiológica y motivos de consulta.

BACKGROUND: Teenager counseling to recognize risks and reinforce strengths is carried out in a primary care outpatient clinic since 2003. AIM: To describe the epidemiology and causes for consultation in this teenage counseling program. MATERIAL AND METHODS: Retrospective review of the records of 116 teenagers (median age 13 years, 67% females) that received teenager counseling. RESULTS: Seventy percent of women and 50% of men came from nuclear families. More than two thirds were primogenital. Most adolescents were accompanied by their mother, that were the main adult raw model. Fifty percent had dysfunctional families. All were attending school regularly and 21% of women and 29% of men had repeated a school level. Sixty eight percent of women and 62% of men declared to have a life project. Twenty percent were worried about their physical appearance. Seventy seven percent of women and 62% of men considered themselves as happy. Thirty six percent of women and 14% of men smoked. The figures for alcohol consumption were 21% and 14%, respectively. The causes for consultation were obesity, overweight, unspecific symptoms, behavioral problems, bad school achievement, communication problems or pregnancy. Reasons for counseling were family dysfunction, low self esteem, bad school achievement and information about sexuality. CONCLUSIONS: The information obtained could help to improve the interdisciplinary work and to coordinate counseling with the family and schools.

Evaluación en el tiempo del impacto de las campañas de comunicación social para la prevención del VIH/SIDA / Evaluation in the time of the impact with the campaigns of social communication for the prevention of HIV/AIDS

La Comisión Nacional del SIDA (CONASIDA) fue creada en 1990, teniendo como objetivos la prevención y disminución del impacto del SIDA en la población. Entre sus estrategias destacan las campañas de comunicación social, desarrolladas en 1991, 1993, 1994 y 1997. El objetivo de este estudio, fue evaluar en el tiempo, los cambios en conocimiento, actitudes y conductas de la población chilena frente al SIDA, en relación con las campañas realizadas por la Comisión. Cada campaña fue revizada y analizada, en cuanto a objetivos, metodología, muestra e instrumentos utilizados, buscando los aspectos comparables. Finalmente, se trabajó con las campañas de 1991-92 y 1993, y con una evaluación previa a la primera, las cuales tuvieron como objetivo informar y crear conciencia del riesgo, pero no cambiar conductas. Se observó aumento significativo en los conocimientos de la población, respecto a formas de transmisión y prevención. La información contribuyó a "desmitificar" y problablemente aumentó el uso de métodos de prevención. Se observa una falta de continuidad para evaluar las campañas, debido a que se utilizaron distintas metodologías. Parece importante mantener, a futuro, la forma de evaluar los resultados de las campañas que se emprendan