589,492 research outputs found
Finite-temperature effects on the superfluid Bose-Einstein condensation of confined ultracold atoms in three-dimensional optical lattices
We discuss the finite-temperature phase diagram in the three-dimensional
Bose-Hubbard (BH) model in the strong correlation regime, relevant for
Bose-Einstein condensates in optical lattices, by employing a quantum rotor
approach. In systems with strong on site repulsive interactions, the rotor U(1)
phase variable dual to the local boson density emerges as an important
collective field. After establishing the connection between the rotor
construction and the the on--site interaction in the BH model the robust
effective action formalism is developed which allows us to study the superfluid
phase transition in various temperature--interaction regimes
Recommended from our members
Strong correlations and orbital texture in single-layer 1T-TaSe2
Strong electron correlation can induce Mott insulating behaviour and produce intriguing states of matter such as unconventional superconductivity and quantum spin liquids. Recent advances in van der Waals material synthesis enable the exploration of Mott systems in the two-dimensional limit. Here we report characterization of the local electronic properties of single- and few-layer 1T-TaSe2 via spatial- and momentum-resolved spectroscopy involving scanning tunnelling microscopy and angle-resolved photoemission. Our results indicate that electron correlation induces a robust Mott insulator state in single-layer 1T-TaSe2 that is accompanied by unusual orbital texture. Interlayer coupling weakens the insulating phase, as shown by reduction of the energy gap and quenching of the correlation-driven orbital texture in bilayer and trilayer 1T-TaSe2. This establishes single-layer 1T-TaSe2 as a useful platform for investigating strong correlation physics in two dimensions
Collective excitations in electron-hole bilayers
We report a combined analytic and Molecular Dynamics analysis of the
collective mode spectrum of an electron-hole (bipolar) bilayer in the strong
coupling quasi-classical limit. A robust, isotropic energy gap is identified in
the out-of-phase spectra, generated by the combined effect of correlations and
of the excitation of the bound dipoles; the in-phase spectra exhibit a
correlation governed acoustic dispersion for the longitudinal and transverse
modes. Strong nonlinear generation of higher harmonics of the fundamental
dipole oscillation frequency and the transfer of harmonics between different
modes is observed. The mode dispersions in the liquid state are compared with
the phonon spectrum in the crystalline solid phase, reinforcing a coherent
physical picture.Comment: 4 pages, 5 figure
Conductance fluctuations in quasi-two-dimensional systems: a practical view
The universal conductance fluctuations of quasi-two-dimensional systems are
analyzed with experimental considerations in mind. The traditional statistical
metrics of these fluctuations (such as variance) are shown to have large
statistical errors in such systems. An alternative characteristic is
identified, the inflection point of the correlation function in magnetic field,
which is shown to be significantly more useful as an experimental metric and to
give a more robust measure of phase coherence.Comment: 9 pages, 7 figure
Phase Transitions in Operational Risk
In this paper we explore the functional correlation approach to operational
risk. We consider networks with heterogeneous a-priori conditional and
unconditional failure probability. In the limit of sparse connectivity,
self-consistent expressions for the dynamical evolution of order parameters are
obtained. Under equilibrium conditions, expressions for the stationary states
are also obtained. The consequences of the analytical theory developed are
analyzed using phase diagrams. We find co-existence of operational and
non-operational phases, much as in liquid-gas systems. Such systems are
susceptible to discontinuous phase transitions from the operational to
non-operational phase via catastrophic breakdown. We find this feature to be
robust against variation of the microscopic modelling assumptions.Comment: 13 pages, 7 figures. Accepted in Physical Review
Bond-charge Interaction in the extended Hubbard chain
We study the effects of bond-charge interaction (or correlated hopping) on
the properties of the extended ({\it i.e.,} with both on-site () and
nearest-neighbor () repulsions) Hubbard model in one dimension at
half-filling. Energy gaps and correlation functions are calculated by Lanczos
diagonalization on finite systems. We find that, irrespective of the sign of
the bond-charge interaction, , the charge--density-wave (CDW) state is more
robust than the spin--density-wave (SDW) state. A small bond-charge interaction
term is enough to make the differences between the CDW and SDW correlation
functions much less dramatic than when . For and fixed (
is the uncorrelated hopping integral), there is an intermediate phase between a
charge ordered phase and a phase corresponding to singly-occupied sites, the
nature of which we clarify: it is characterized by a succession of critical
points, each of which corresponding to a different density of doubly-occupied
sites. We also find an unusual slowly decaying staggered spin-density
correlation function, which is suggestive of some degree of ordering. No
enhancement of pairing correlations was found for any in the range
examined.Comment: 10 pages, 7 PostScript figures, RevTeX 3; to appear in Phys Rev
- …