529 research outputs found
Strongly Interacting p-wave Fermi Gas in Two-Dimensions: Universal Relations and Breathing Mode
The contact is an important concept that characterizes the universal
properties of a strongly interacting quantum gas. It appears in both
thermodynamic (energy, pressure, etc.) and dynamic quantities (radio-frequency
and Bragg spectroscopies, etc.) of the system. Very recently, the concept of
contact has been extended to higher partial waves, in particular, the p-wave
contacts have been experimentally probed in recent experiment. So far
discussions on p-wave contacts have been limited to three-dimensions. In this
paper, we generalize the p-wave contacts to two-dimensions and derive a series
of universal relations, including the adiabatic relations, high momentum
distribution, virial theorem and pressure relation. At high temperature and low
density limit, we calculated the p-wave contacts explicitly using virial
expansion. A formula which directly connects the shift of the breathing mode
frequency and the p-wave contacts are given in a harmonically trapped system.
Finally, we also derive the relationships between interaction parameters in
three and two dimensional Fermi gas and discuss possible experimental
realization of two dimensional Fermi gas with p-wave interactions.Comment: 12 pages,4 figur
Quantum Phases and Collective Excitations in Bose-Hubbard Models with Staggered Magnetic Flux
We study the quantum phases of a Bose-Hubbard model with staggered magnetic
flux in two dimensions, as has been realized recently [Aidelsburger {\it et
al.}, PRL, {\bf 107}, 255301 (2011)]. Within mean field theory, we show how the
structure of the condensates evolves from weak to strong coupling limit,
exhibiting a tricritical point at the Mott-superfluid transition. Non-trivial
topological structures (Dirac points) in the quasi-particle (hole) excitations
in the Mott state are found within random phase approximation and we discuss
how interaction modifies their structures. Excitation gap in the Mott state
closes at different points when approaching the superfluid states,
which is consistent with the findings of mean field theory.Comment: 5 pages, 3 figure
Effective theory and universal relations for Fermi gases near a -wave interaction resonance
In this work, we present an effective field theory to describe a
two-component Fermi gas near a -wave interaction resonance. The effective
field theory is renormalizable by matching with the low energy -wave
scattering phase shift. Based on the effective field theory, we derive
universal properties of the Fermi gas by the operator product expansion method.
We find that beyond the contacts defined by adiabatic theorems, the asymptotic
expressions of the momentum distribution and the Raman spectroscopy involve two
extra contacts which provide additional information of correlations of the
system. Our formalism sets the stage for further explorations of many-body
effects in a -wave resonant Fermi gas. Finally we generalise our effective
field theory for interaction resonances of arbitrary higher partial waves.Comment: revised versio
Evidence for correlated states in a cluster of bosons with Rashba spin-orbit coupling
We study the ground state properties of spin-half bosons subjected to the
Rashba spin-orbit coupling in two dimensions. Due to the enhancement of the low
energy density of states, it is expected that the effect of interaction becomes
more important. After reviewing several possible ideal condensed states, we
carry out an exact diagonalization calculation for a cluster of the bosons in
the presence of strong spin-orbit coupling on a two-dimensional disk and reveal
strong correlations in its ground state. We derive a low-energy effective
Hamiltonian to understand how states with strong correlations become
energetically more favorable than the ideal condensed states.Comment: 23 pages, 6 figure
Mott-Superfluid Transition for Spin-Orbit Coupled Bosons in One-Dimensional Optical Lattices
We study the effects of spin-orbit coupling on the Mott-superfluid transition
of bosons in a one-dimensional optical lattice. We determine the strong
coupling magnetic phase diagram by a combination of exact analytic and
numerical means. Smooth evolution of the magnetic structure into the superfluid
phases are investigated with the density matrix renormalization group
technique. Novel magnetic phases are uncovered and phase transitions between
them within the superfluid regime are discussed. Possible experimental
detection are discussed.Comment: 5 pages, 4 figure
Fluctuation Effects on the Transport Properties of Unitary Fermi Gases
In this letter, we investigate the fluctuation effects on the transport
properties of unitary Fermi gases in the vicinity of the superfluid transition
temperature . Based on the time-dependent Ginzburg-Landau formalism of the
BEC-BCS crossover, we investigate both the residual resistivity below
induced by phase slips and the paraconductivity above due to pair
fluctuations. These two effects have been well studied in the weak coupling BCS
superconductor, and here we generalize them to the unitary regime of ultracold
Fermi gases. We find that while the residual resistivity below increases
as one approaches the unitary limit, consistent with recent experiments, the
paraconductivity exhibits non-monotonic behavior. Our results can be verified
with the recently developed transport apparatus using mesoscopic channels.Comment: 8 pages and 4 figures including supplementary material
Evolution of Higgs mode in a Fermion Superfluid with Tunable Interactions
In this letter we present a coherent picture for the evolution of Higgs mode
in both neutral and charged -wave fermion superfluids, as the strength of
attractive interaction between fermions increases from the BCS to the BEC
regime. In the case of neutral fermionic superfluid, such as ultracold
fermions, the Higgs mode is pushed to higher energy while at the same time,
gradually loses its spectral weight as interaction strength increases toward
the BEC regime, because the system is further tuned away from Lorentz
invariance. On the other hand, when damping is taken into account, Higgs mode
is significantly broadened due to coupling to phase mode in the whole BEC-BCS
crossover. In the charged case of electron superconductor, the Anderson-Higgs
mechanism gaps out the phase mode and suppresses the coupling between the Higgs
and the phase modes, and consequently, stabilizes the Higgs mode.Comment: 5 figures, 9 pages, including supplementary materia
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