289 research outputs found
Strong-coupling expansion for the two-species Bose-Hubbard model
To analyze the ground-state phase diagram of Bose-Bose mixtures loaded into
-dimensional hypercubic optical lattices, we perform a strong-coupling
power-series expansion in the kinetic energy term (plus a scaling analysis) for
the two-species Bose-Hubbard model with onsite boson-boson interactions. We
consider both repulsive and attractive interspecies interaction, and obtain an
analytical expression for the phase boundary between the incompressible Mott
insulator and the compressible superfluid phase up to third order in the
hoppings. In particular, we find a re-entrant quantum phase transition from
paired superfluid (superfluidity of composite bosons, i.e. Bose-Bose pairs) to
Mott insulator and again to a paired superfluid in all one, two and three
dimensions, when the interspecies interaction is sufficiently large and
attractive. We hope that some of our results could be tested with ultracold
atomic systems.Comment: 8 pages, 4 figures, and 2 tables (published version
Stripe-ordered superfluid and supersolid phases in attractive Hofstadter-Hubbard model
We use microscopic Bogoliubov-de Gennes formalism to explore the ground-state
phase diagram of the single-band attractive Hofstadter-Hubbard model on a
square lattice. We show that the interplay between the Hofstadter butterfly and
superfluidity breaks spatial symmetry, and gives rise to stripe-ordered
superfluid and supersolid phases in large parameter spaces. We also discuss the
effects of a trapping potential and comment on the viability of observing
stripe-ordered phases with cold Fermi gases.Comment: 4+ pages with 3 figures; to appear in PRA as R
Vortex line in spin-orbit coupled atomic Fermi gases
It has recently been shown that the spin-orbit coupling gives rise to
topologically-nontrivial and thermodynamically-stable gapless superfluid phases
when the pseudo-spin populations of an atomic Fermi gas is imbalanced, with the
possibility of featuring Majorana zero-energy quasiparticles. In this paper, we
consider a Rashba-type spin-orbit coupling, and use the Bogoliubov-de Gennes
formalism to analyze a single vortex line along a finite cylinder with a
periodic boundary condition. We show that the signatures for the appearance of
core- and edge-bound states can be directly found in the density of
single-particle states and particle-current density. In particular, we find
that the pseudo-spin components counterflow near the edge of the cylinder, the
strength of which increases with increasing spin-orbit coupling.Comment: 7 pages with 6 figures; minor change
Trapped Fermi gases with Rashba spin-orbit coupling in two dimensions
We use the Bogoliubov-de Gennes formalism to analyze harmonically trapped
Fermi gases with Rashba-type spin-orbit coupling in two dimensions. We consider
both population-balanced and -imbalanced Fermi gases throughout the BCS-BEC
evolution, and study the effects of spin-orbit coupling on the spontaneously
induced countercirculating mass currents and the associated intrinsic angular
momentum. In particular, we find that even a small spin-orbit coupling
destabilizes Fulde-Ferrel-Larkin-Ovchinnikov (FFLO)-type spatially modulated
superfluid phases as well as the phase-separated states against the polarized
superfluid phase. We also show that the continuum of quasiparticle and
quasihole excitation spectrum can be connected by zero, one or two discrete
branches of interface modes, depending on the number of interfaces between a
topologically trivial phase (e.g. locally unpolarized/low-polarized superfluid
or spin-polarized normal) and a topologically nontrivial one (e.g. locally
high-polarized superfluid) that may be present in a trapped system.Comment: 7 pages with 4 figure
Attractive Hofstadter-Hubbard model with imbalanced chemical and vector potentials
We study the interplay between the Hofstadter butterfly, strong interactions
and Zeeman field within the mean-field Bogoliubov-de Gennes theory in real
space, and explore the ground states of the attractive single-band
Hofstadter-Hubbard Hamiltonian on a square lattice, including the exotic
possibility of imbalanced vector potentials. We find that the cooperation
between the vector potential and superfluid order breaks the spatial symmetry
of the system, and flourish stripe-ordered Fulde-Ferrell-Larkin-Ovchinnikov
(FFLO)-like superfluid and supersolid phases that can be distinguished and
characterized according to their coexisting pair-density (PDW), charge-density
(CDW) and spin-density (SDW) wave orders. We also discuss confined systems and
comment on the likelihood of observing such stripe-ordered phases by loading
neutral atomic Fermi gases on laser-induced optical lattices under
laser-generated artificial gauge fields.Comment: 12 pages and 13 figures; longer version of arXiv:1406.689
Isothermal sweep theorems for ultra-cold quantum gases in a canonical ensemble
After deriving the isothermal Hellmann-Feynman theorem (IHFT) that is
suitable for mixed states in a canonical ensemble, we use this theorem to
obtain the isothermal magnetic-field sweep theorems for the free, average and
trapping energies, and for the entropy, specific heat, pressure and atomic
compressibility of strongly-correlated ultra-cold quantum gases. In particular,
we apply the sweep theorems to two-component Fermi gases in the
weakly-interacting BCS and BEC limits, showing that the temperature dependence
of the contact parameter can be determined by the variation of either the
entropy or specific heat with respect to the scattering length. We also use the
IHFT to obtain the Virial theorem in a canonical ensemble, and discuss its
implications for quantum gases.Comment: 6 pages (added more discussion
- …