Bose-Hubbard model on a star lattice

We analyze the Bose-Hubbard model of hardcore bosons with nearest neighbor hopping and repulsive interactions on a star lattice using both quantum Monte Carlo simulation and dual vortex theory. We obtain the phase diagram of this model as a function of the chemical potential and the relative strength of hopping and interaction. In the strong interaction regime, we find that the Mott phases of the model at 1/2 and 1/3 fillings, in contrast to their counterparts on square, triangular, and Kagome lattices, are either translationally invariant resonant valence bond (RVB) phases with no density-wave order or have coexisting density-wave and RVB orders. We also find that upon increasing the relative strength of hopping and interaction, the translationally invariant Mott states undergo direct second order superfluid-insulator quantum phase transitions. We compute the critical exponents for these transitions and argue using the dual vortex picture that the transitions, when approached through the tip of the Mott lobe, belong to the inverted XY universality class.Comment: 10 pages, 18 figures, minor changes, two references adde

Topological transition in disordered planar matching: combinatorial arcs expansion

In this paper, we investigate analytically the properties of the disordered Bernoulli model of planar matching. This model is characterized by a topological phase transition, yielding complete planar matching solutions only above a critical density threshold. We develop a combinatorial procedure of arcs expansion that explicitly takes into account the contribution of short arcs, and allows to obtain an accurate analytical estimation of the critical value by reducing the global constrained problem to a set of local ones. As an application to a toy representation of the RNA secondary structures, we suggest generalized models that incorporate a one-to-one correspondence between the contact matrix and the RNA-type sequence, thus giving sense to the notion of effective non-integer alphabets.Comment: 28 pages, 6 figures, published versio

Domain Dynamics in Piezoresponse Force Microscopy: Quantitative Deconvolution and Hysteresis Loop Fine Structure

Domain dynamics in the Piezoresponse Force Spectroscopy (PFS) experiment is studied using the combination of local hysteresis loop acquisition with simultaneous domain imaging. The analytical theory for PFS signal from domain of arbitrary cross-section is developed and used for the analysis of experimental data on Pb(Zr,Ti)O3 polycrystalline films. The results suggest formation of oblate domain at early stage of the domain nucleation and growth, consistent with efficient screening of depolarization field within the material. The fine structure of the hysteresis loop is shown to be related to the observed jumps in the domain geometry during domain wall propagation (nanoscale Barkhausen jumps), indicative of strong domain-defect interactions.Comment: 17 pages, 3 figures, 2 Appendices, to be submmited to Appl. Phys. Let

Generation of high-energy soliton-like pulses in 1.9–2.5 µ m spectral domain

Abstract: We experimentally demonstrate the generation of soliton-like pulses with 195–230 fs duration and energy up to 20 nJ in the spectral region of 1.9–2.5 µm directly from the Tm-doped all-fiber MOPA laser. The emerged Raman solitons generated directly in the fiber amplifier exhibit unusual dynamics and spectral properties forming a supercontinuum without conventional gaps between Stokes pulses. Namely, at the output powers above 2 W, in addition to conventional soliton spectral peaks beyond 2.3 μm, we observe high spectral density over an extended range of 1.95–2.23 μm corresponding to a coherent structure that to the best of our knowledge differs from any previously observed supercontinuum regimes. The average optical power of the fiber laser is at the 3-W level, whereas the estimated peak power reached the 80-kW level. Such a relatively simple laser system with high spectral density is a promising light source for various applications ranging from advanced comb spectroscopy to ultra-fast photonics

High-energy Atmospheric Muon Flux Expected at India-Based Neutrino Observatory

We calculate the zenith-angle dependence of conventional and prompt high-energy muon fluxes at India-Based Neutrino Observatory (INO) depth. This study demonstrates a possibility to discriminate models of the charm hadroproduction including the low-x QCD behaviour of hadronic cross-sections relevant at very high energies.Comment: 10 pages. 8 figures, 3 table

High Power Gamma-Ray Flash Generation in Ultra Intense Laser-Plasma Interaction

When high-intensity laser interaction with matter enters the regime of dominated radiation reaction, the radiation losses open the way for producing short pulse high power gamma ray flashes. The gamma-ray pulse duration and divergence are determined by the laser pulse amplitude and by the plasma target density scale length. On the basis of theoretical analysis and particle-in-cell simulations with the radiation friction force incorporated, optimal conditions for generating a gamma-ray flash with a tailored overcritical density target are found.Comment: 12 pages, 5 figures Accepted for publication in Physical Review Letters (this http://prl.aps.org/

Some problems of precise measurements of heat transfer coefficients in glass melts : Part 1. Measurements of effective conductivity

In the paper the method of measurements of the so-called effective conductivity of glass melts basing on characteristic of temperature gradient in a molten glass inside a refractory tank is analyzed. For this purpose a computer model based on the solution of the radiative transfer equation in a semitransparent medium was used. Among the papers on effective conductivity measurements published so far, only two contained enough numerical information on the details of measurement which permitted to perform the corresponding calculations. The authors of the present paper show what particular defects of experimental procedure could be the reason of surprising results reported in these publications, namely that the measured effective conductivity coefficient of a number of glasses was found to be lower than the radiative conductivity alone