Phase Diagram of the Bose-Hubbard Model with T_3 symmetry

In this paper we study the quantum phase transition between the insulating and the globally coherent superfluid phases in the Bose-Hubbard model with T_3 structure, the "dice lattice". Even in the absence of any frustration the superfluid phase is characterized by modulation of the order parameter on the different sublattices of the T_3 structure. The zero-temperature critical point as a function of a magnetic field shows the characteristic "butterfly" form. At fully frustration the superfluid region is strongly suppressed. In addition, due to the existence of the Aharonov-Bohm cages at f=1/2, we find evidence for the existence of an intermediate insulating phase characterized by a zero superfluid stiffness but finite compressibility. In this intermediate phase bosons are localized due to the external frustration and the topology of the T_3 lattice. We name this new phase the Aharonov-Bohm (AB) insulator. In the presence of charge frustration the phase diagram acquires the typical lobe-structure. The form and hierarchy of the Mott insulating states with fractional fillings, is dictated by the particular topology of the T_3 lattice. The results presented in this paper were obtained by a variety of analytical methods: mean-field and variational techniques to approach the phase boundary from the superconducting side, and a strongly coupled expansion appropriate for the Mott insulating region. In addition we performed Quantum Monte Carlo simulations of the corresponding (2+1)D XY model to corroborate the analytical calculations with a more accurate quantitative analysis. We finally discuss experimental realization of the T_3 lattice both with optical lattices and with Josephson junction arrays.Comment: 16 pages, 17 figure

Observation of Ising-like critical fluctuations in frustrated Josephson junction arrays with modulated coupling energies

We report the results of ac sheet conductance measurements performed on fully frustrated square arrays of Josephson junctions whose coupling energy is periodically modulated in one of the principal lattice directions. Such systems are predicted to exhibit two distinct transitions: a low-temperature Ising-like transition triggered by the proliferation of domain walls and a high-temperature transition driven by the vortex unbinding mechanism of the Beresinskii-Kosterlitz-Thouless (BKT) theory. Both the superfluid and dissipative components of the conductance are found to exhibit features which unambiguously demonstrate the existence of a double transition whose properties are consistent with the Ising-BKT scenario.Comment: To be published in Physica C (Proceedings of the 2nd European Conference in School Format 'Vortex Matter in Superconductors'

Dynamic ordering of driven vortex matter in the peak effect regime of amorphous MoGe films and 2H-NbSe2 crystals

Dynamic ordering of driven vortex matter has been investigated in the peak effect regime of both amorphous MoGe films and 2H-NbSe2 crystals by mode locking (ML) and dc transport measurements. ML features allow us to trace how the shear rigidity of driven vortices evolves with the average velocity. Determining the onset of ML resonance in different magnetic fields and/or temperatures, we find that the dynamic ordering frequency (velocity) exhibits a striking divergence in the higher part of the peak effect regime. Interestingly, this phenomenon is accompanied by a pronounced peak of dynamic critical current. Mapping out field-temperature phase diagrams, we find that divergent points follow well the thermodynamic melting curve of the ideal vortex lattice over wide field and/or temperature ranges. These findings provide a link between the dynamic and static melting phenomena which can be distinguished from the disorder induced peak effect.Comment: 9 pages, 6 figure

Mode locking of vortex matter driven through mesoscopic channels

We investigated the driven dynamics of vortices confined to mesoscopic flow channels by means of a dc-rf interference technique. The observed mode-locking steps in the $IV$-curves provide detailed information on how the number of rows and lattice structure in the channel change with magnetic field. Minima in flow stress occur when an integer number of rows is moving coherently, while maxima appear when incoherent motion of mixed $n$ and $n\pm 1$ row configurations is predominant. Simulations show that the enhanced pinning at mismatch originates from quasi-static fault zones with misoriented edge dislocations induced by disorder in the channel edges.Comment: some minor changes were made, 4 pages, 4 figures, accepted for publication in Phys. Rev. Let

Modalidades de explotación, procesamiento y consumo de pinnípedos en la margen meridional de Tierra del Fuego

En términos generales, en cuanto al modo de subsistencia, es posible sostener que los pinnípedos fueron una de las fuentes energéticas principales de los grupos que habitaron el sur del archipiélago fueguino. No obstante, se observa variabilidad temporo-espacial en la importancia económica de estas presas en la dieta de los cazadores-recolectores-pescadores de esta amplia región. En algunos trabajos se avanzó sobre aspectos relacionados con la explotación de estos animales, particularmente en la región central de la costa norte canal Beagle: dos contextos del Holoceno medio, el Segundo Componente de Túnel I (Schiavini 1990, 1993) y el Segundo Componente de Imiwaia I. Sin embargo, en la mayoría de los conjuntos de la costa sur del archipiélago fueguino -especialmente en Moat, Península Mitre y en la Isla delos Estados- se desconocen las posibles pautas de aprovisionamiento, procesamiento, transporte y consumo seleccionadas por los grupos humanos que habitaron la región, y si estas variaron a lo largo del tiempo. El objetivo principal de la presente tesis es analizar en perspectiva comparativa las modalidades de explotación de pinnípedos en la costa sur de Tierra del Fuego y en la Isla de los Estados, y sus variaciones a lo largo del Holoceno.Fil: Martinoli, Maria Paz. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Austral de Investigaciones Científicas; Argentina. Universidad de Buenos Aires; Argentin

Pinniped processing and consumption patterns in southern coast of Tierra del Fuego and Isla de los Estados: A comparative analysis

Si bien los pinnípedos (Arctocephalus australis y Otaria flavescens) constituyeron uno de los principales recursos para las cazadores-recolectores del sur de Tierra del Fuego e Isla de los Estados durante el Holoceno, existió variabilidad en la interacción humanos-pinnípedos en ese espacio. Tales variaciones pueden relacionarse con el acceso diferencial a los apostaderos reproductivos en las costas del archipiélago fueguino. El análisis de los restos de pinnípedos de tres sitios del Holoceno tardío ubicados en sectores costeros distintos (canal Beagle, sur de Península Mitre e Isla de los Estados) muestra que mientras en el sitio del canal Beagle dominan los A. australis hembras adultas con gran incidencia de marcas de procesamiento, en los conjuntos del sur de Península Mitre e Isla de los Estados están mayormente representados cachorros y machos adultos de ambas especies y las modificaciones culturales afectan en porcentajes bajos a los conjuntos. Aunque los tres perfiles de edad y sexo indican el aprovechamiento de animales en tierra, la disponibilidad de loberías reproductivas en cercanías de los sitios en el sector suroriental del archipiélago fueguino habría favorecido la captura de presas de mayor tamaño (O. flavescens machos adultos) con un costo de aprovisionamiento menor, lo cual implicó un procesamiento poco integral de las presas.Pinnipeds (Arctocephalus australis and Otaria flavescens) were an important food source for hunter-gatherers along the southern coast of Tierra del Fuego and Isla de los Estados. Even so, there was variability in the human-pinniped interactions recorded for this area. These variations probably relate to the distribution of rookeries across the Fuegian archipelago. Pinniped bone remains from three Late Holocene sites located in different coastal areas (Beagle Channel, Peninsula Mitre and Isla de los Estados) demonstrate that at the Beagle Channel site A. australis adult females predominated, with the bones exhibiting considerable processing marks, meanwhile at Peninsula Mitre and Isla de los Estados, mostly neonates and adult males of both species were represented, the assemblages also had few butchery marks. Age and sex profiles at the three sites indicate that these prey were captured on land. Nevertheless, the availability of rookeries near the sites in the south-eastern Fuegian archipelago, allowed them to catch larger animals (O. flavescens adult males), which implied lower foraging cost, involving fewer processing activities

Magnetoinductance of Josephson junction array with frozen vortex diffusion

The dependence of sheet impedance of a Josephson junction array on the applied magnetic field is investigated in the regime when vortex diffusion between array plaquettes is effectively frozen due to low enough temperature. The field dependent contribution to sheet inductance is found to be proportional to f*ln(1/f), where f<<1 is the magnitude of the field expressed in terms of flux quanta per plaquette.Comment: 5 pages, no figure

Pokrovsky-Talapov Model at finite temperature: a renormalization-group analysis

We calculate the finite-temperature shift of the critical wavevector $Q_{c}$ of the Pokrovsky-Talapov model using a renormalization-group analysis. Separating the Hamiltonian into a part that is renormalized and one that is not, we obtain the flow equations for the stiffness and an arbitrary potential. We then specialize to the case of a cosine potential, and compare our results to well-known results for the sine-Gordon model, to which our model reduces in the limit of vanishing driving wavevector Q=0. Our results may be applied to describe the commensurate-incommensurate phase transition in several physical systems and allow for a more realistic comparison with experiments, which are always carried out at a finite temperature