79 research outputs found
Spin effects in Bose-Glass phases
We study the mechanism of formation of Bose glass (BG) phases in the spin-1
Bose Hubbard model when diagonal disorder is introduced. To this aim, we
analyze first the phase diagram in the zero-hopping limit, there disorder
induces superposition between Mott insulator (MI) phases with different filling
numbers. Then BG appears as a compressible but still insulating phase. The
phase diagram for finite hopping is also calculated with the Gutzwiller
approximation. The bosons' spin degree of freedom introduces another scattering
channel in the two-body interaction modifying the stability of MI regions with
respect to the action of disorder. This leads to some peculiar phenomena such
as the creation of BG of singlets, for very strong spin correlation, or the
disappearance of BG phase in some particular cases where fluctuations are not
able to mix different MI regions
Spin-structures of N-boson systems with nonzero spins - an analytically solvable model with pairing force
A model is proposed to study the possible pairing structures of N-boson
systems with nonzero spin. Analytical solutions have been obtained. The
emphasis is placed on the spin-structures of ground states with attractive or
repulsive pairing force, and with or without the action of a magnetic field. A
quantity (an analogue of the two-body density function) is defined to study the
spin-correlation between two bosons in N-body systems. The excitation of the
system has also been studied.Comment: 10 pages, 2 figures, accepted by Few-Body System
Pair excitations and parameters of state of imbalanced Fermi gases at finite temperatures
The spectra of low-lying pair excitations for an imbalanced two-component
superfluid Fermi gas are analytically derived within the path-integral
formalism taking into account Gaussian fluctuations about the saddle point. The
spectra are obtained for nonzero temperatures, both with and without imbalance,
and for arbitrary interaction strength. On the basis of the pair excitation
spectrum, we have calculated the thermodynamic parameters of state of cold
fermions and the first and second sound velocities. The parameters of pair
excitations show a remarkable agreement with the Monte Carlo data and with
experiment.Comment: 14 pages, 5 figure
Efimov Trimers near the Zero-crossing of a Feshbach Resonance
Near a Feshbach resonance, the two-body scattering length can assume any
value. When it approaches zero, the next-order term given by the effective
range is known to diverge. We consider the question of whether this divergence
(and the vanishing of the scattering length) is accompanied by an anomalous
solution of the three-boson Schr\"odinger equation similar to the one found at
infinite scattering length by Efimov. Within a simple zero-range model, we find
no such solutions, and conclude that higher-order terms do not support Efimov
physics.Comment: 8 pages, no figures, final versio
First record of Rhabdoceras suessi (Ammonoidea, Late Triassic) from the Transylvanian Triassic Series of the Eastern Carpathians (Romania) and a review of its biochronology, paleobiogeography and paleoecology
Abstract
The occurrence of the heteromorphic ammonoid Rhabdoceras suessi Hauer, 1860, is recorded for the first time in the Upper Triassic limestone of the Timon-Ciungi olistolith in the Rarău Syncline, Eastern Carpathians. A single specimen of Rhabdoceras suessi co-occurs with Monotis (Monotis) salinaria that constrains its occurrence here to the Upper Norian (Sevatian 1). It is the only known heteromorphic ammonoid in the Upper Triassic of the Romanian Carpathians. Rhabdoceras suessi is a cosmopolitan species widely recorded in low and mid-paleolatitude faunas. It ranges from the Late Norian to the Rhaetian and is suitable for high-resolution worldwide correlations only when it co-occurs with shorter-ranging choristoceratids, monotid bivalves, or the hydrozoan Heterastridium. Formerly considered as the index fossil for the Upper Norian (Sevatian) Suessi Zone, by the latest 1970s this species lost its key biochronologic status among Late Triassic ammonoids, and it generated a controversy in the 1980s concerning the status of the Rhaetian stage. New stratigraphic data from North America and Europe in the subsequent decades resulted in a revised ammonoid biostratigraphy for the uppermost Triassic, the Rhaetian being reinstalled as the topmost stage in the current standard timescale of the Triassic. The geographic distribution of Rhabdoceras is compiled from published worldwide records, and its paleobiogeography and paleoecology are discussed
- …