697 research outputs found
Persistent supersolid phase of hard-core bosons on the triangular lattice
We study hard-core bosons with unfrustrated hopping () and nearest
neighbour repulsion () on the triangular lattice. At half-filling, the
system undergoes a zero temperature () quantum phase transition from a
superfluid phase at small to a supersolid at in units of
. This supersolid phase breaks the lattice translation symmetry in a
characteristic pattern, and is remarkably
stable--indeed, a smooth extrapolation of our results indicates that the
supersolid phase persists for arbitrarily large .Comment: 4 pages, 5 figures, two column forma
Long term Ultra-Violet Variability of Seyfert galaxies
Flux variability is one of the defining characteristics of Seyfert galaxies,
a class of active galactic nuclei (AGN). Though these variations are observed
over a wide range of wavelengths, results on their flux variability
characteristics in the ultra-violet (UV) band are very limited. We present here
the long term UV flux variability characteristics of a sample of fourteen
Seyfert galaxies using data from the International Ultraviolet Explorer
acquired between 1978 and 1995. We found that all the sources showed flux
variations with no statistically significant difference in the amplitude of UV
flux variation between shorter and longer wavelengths. Also, the flux
variations between different near-UV (NUV, 1850 - 3300 A) and far-UV (FUV, 1150
- 2000 A) passbands in the rest frames of the objects are correlated with no
time lag. The data show indications of (i) a mild negative correlation of UV
variability with bolometric luminosity and (ii) weak positive correlation
between UV variability and black hole mass. At FUV, about 50% of the sources
show a strong correlation between spectral indices and flux variations with a
hardening when brightening behaviour, while for the remaining sources the
correlation is moderate. In NUV, the sources do show a harder when brighter
trend, however, the correlation is either weak or moderate.Comment: Accepted by Journal of Astrophysics and Astronom
Salinity tolerance and fishery of mud shrimp Solenocera crassicornis (H. Milne Edwards) in the coastal waters of Mumbai
Salinity tolerance of mud shrimp Solenocera crassicornis investigated at different salinities ranging
from 15‰ to 55‰ showed that shrimps in the salinity range 30‰ - 42‰ survived but those in lower and
higher salinities died soon after the transfer. Ionic concentration in the hemolymph and free amino acids
in the body muscle in response to different salinity ranges showed hypo-regulation initially but later
became hyposmotic to the medium and died eventually when the salinity decreased. The abundance of
shrimp showed inverse relationship with rainfall and consequent lowering of salinity in the inshore
waters. The study showed that S. crassicornis can regulate osmotic and ionic concentrations of body
fluids efficiently in the salinity range of 30 - 42‰ but unlike euryhaline penaeid shrimps it is a poor
regulator at lower salinities and therefore it migrates offshore during monsoon months
Emergent Moments and Random Singlet Physics in a Majorana Spin Liquid
We exhibit an exactly solvable example of a SU(2) symmetric Majorana spin liquid phase, in which quenched disorder leads to random-singlet phenomenology of emergent magnetic moments. More precisely, we argue that a strong-disorder fixed point controls the low temperature susceptibility chi(T) of an exactly solvable S = 1/2 model on the decorated honeycomb lattice with vacancy and/or bond disorder, leading to chi(T) = C/T + DT alpha(T)-1, where alpha(T) -> 0 slowly as the temperature T -> 0. The first term is a Curie tail that represents the emergent response of vacancy-induced spin textures spread over many unit cells: it is an intrinsic feature of the site-diluted system, rather than an extraneous effect arising from isolated free spins. The second term, common to both vacancy and bond disorder [with different alpha(T) in the two cases] is the response of a random singlet phase, familiar from random antiferromagnetic spin chains and the analogous regime in phosphorus-doped silicon (Si:P)
Emergent moments and random singlet physics in a Majorana spin liquid
We exhibit an exactly solvable example of a SU(2) symmetric Majorana spin
liquid phase, in which quenched disorder leads to random-singlet phenomenology.
More precisely, we argue that a strong-disorder fixed point controls the low
temperature susceptibility of an exactly solvable model on
the decorated honeycomb lattice with quenched bond disorder and/or vacancies,
leading to where
as . The first term is a Curie tail
that represents the emergent response of vacancy-induced spin textures spread
over many unit cells: it is an intrinsic feature of the site-diluted system,
rather than an extraneous effect arising from isolated free spins. The second
term, common to both vacancy and bond disorder (with different in
the two cases) is the response of a random singlet phase, familiar from random
antiferromagnetic spin chains and the analogous regime in phosphorus-doped
silicon (Si:P).Comment: two-column format; 4+pages; 3 figure
Dulmage-Mendelsohn percolation: Geometry of maximally-packed dimer models and topologically-protected zero modes on diluted bipartite lattices
The classic combinatorial construct of {\em maximum matchings} probes the
random geometry of regions with local sublattice imbalance in a site-diluted
bipartite lattice. We demonstrate that these regions, which host the monomers
of any maximum matching of the lattice, control the localization properties of
a zero-energy quantum particle hopping on this lattice. The structure theory of
Dulmage and Mendelsohn provides us a way of identifying a complete and
non-overlapping set of such regions. This motivates our large-scale
computational study of the Dulmage-Mendelsohn decomposition of site-diluted
bipartite lattices in two and three dimensions. Our computations uncover an
interesting universality class of percolation associated with the end-to-end
connectivity of such monomer-carrying regions with local sublattice imbalance,
which we dub {\em Dulmage-Mendelsohn percolation}. Our results imply the
existence of a monomer percolation transition in the classical statistical
mechanics of the associated maximally-packed dimer model and the existence of a
phase with area-law entanglement entropy of arbitrary many-body eigenstates of
the corresponding quantum dimer model. They also have striking implications for
the nature of collective zero-energy Majorana fermion excitations of bipartite
networks of Majorana modes localized on sites of diluted lattices, for the
character of topologically-protected zero-energy wavefunctions of the bipartite
random hopping problem on such lattices, and thence for the corresponding
quantum percolation problem, and for the nature of low-energy magnetic
excitations in bipartite quantum antiferromagnets diluted by a small density of
nonmagnetic impurities.Comment: minor typos and errors fixed; further clarifications added. no
substantive changes in result
Griffiths Effects in Random Heisenberg Antiferromagnetic S=1 Chains
I consider the effects of enforced dimerization on random Heisenberg
antiferromagnetic S=1 chains. I argue for the existence of novel Griffiths
phases characterized by {\em two independent dynamical exponents} that vary
continuously in these phases; one of the exponents controls the density of
spin-1/2 degrees of freedom in the low-energy effective Hamiltonian, while the
other controls the corresponding density of spin-1 degrees of freedom.
Moreover, in one of these Griffiths phases, the system has very different low
temperature behavior in two different parts of the phase which are separated
from each other by a sharply defined crossover line; on one side of this
crossover line, the system `looks' like a S=1 chain at low energies, while on
the other side, it is best thought of as a chain. A strong-disorder RG
analysis makes it possible to analytically obtain detailed information about
the low temperature behavior of physical observables such as the susceptibility
and the specific heat, as well as identify an experimentally accessible
signature of this novel crossover.Comment: 16 pages, two-column PRB format; 5 figure
Crystallization of SrCO<SUB>3</SUB> within thermally evaporated fatty acid films: unusual morphology of crystal aggregates
Reaction of CO2 with electrostatically entrapped Sr2+ ions within thermally evaporated stearic acid films leads to the in-situ growth of SrCO3 crystals in highly organized assemblies, the organization possibly occurring due to hydrophobic association of the crystallites covered by a monolayer of stearic acid
Non-equilibrium Gross-Pitaevskii dynamics of boson lattice models
Motivated by recent experiments on trapped ultra-cold bosonic atoms in an
optical lattice potential, we consider the non-equilibrium dynamic properties
of such bosonic systems for a number of experimentally relevant situations.
When the number of bosons per lattice site is large, there is a wide parameter
regime where the effective boson interactions are strong, but the ground state
remains a superfluid (and not a Mott insulator): we describe the conditions
under which the dynamics in this regime can be described by a discrete
Gross-Pitaevskii equation. We describe the evolution of the phase coherence
after the system is initially prepared in a Mott insulating state, and then
allowed to evolve after a sudden change in parameters places it in a regime
with a superfluid ground state. We also consider initial conditions with a "pi
phase" imprint on a superfluid ground state (i.e. the initial phases of
neighboring wells differ by pi), and discuss the subsequent appearance of
density wave order and "Schrodinger cat" states.Comment: 16 pages, 11 figures; (v2) added reference
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