1,126 research outputs found
Induced interaction in a spin-polarized Fermi gas
We study the effect of the induced interaction on the superfluidtransition
temperature of a spin-polarized Fermi gas. In the BCS limit, the polarization
is very small in the superfluid state, and the effect of the induced
interaction is almost the same as in the spin-balanced case. The temperature Tt
and the polarization Pt of the tricritical point are both reduced from
mean-field results by a factor about 2.22. This reduction is also significant
beyond the BCS limit. In the unitary limit, we find (Pt,Tt/TF)=(0.42,0.16), in
comparison with mean-field and experimental results.Comment: 6 pages, 2 figure
Spin-Orbit Coupled Fermi Gases across a Feshbach Resonance
In this letter we study both ground state properties and the superfluid
transition temperature of a spin-1/2 Fermi gas across a Feshbach resonance with
a synthetic spin-orbit coupling, using mean-field theory and exact solution of
two-body problem. We show that a strong spin-orbit coupling can significantly
enhance the pairing gap for 1/(k_F a_s)<=0 due to increased density-of-state.
Strong spin-orbit coupling also significantly enhances the superfluid
transition temperature when 1/(k_F a_s)<=0, while suppresses it slightly when
1/(k_F a_s)>0. The universal interaction energy and pair size at resonance are
also discussed.Comment: 4+3 pages, 4 figures, supplementary material adde
Stability Condition of a Strongly Interacting Boson-Fermion Mixture across an Inter-Species Feshbach Resonance
We study the properties of dilute bosons immersed in a single component Fermi
sea across a broad boson-fermion Feshbach resonance. The stability of the
mixture requires that the bare interaction between bosons exceeds a critical
value, which is a universal function of the boson-fermion scattering length,
and exhibits a maximum in the unitary region. We calculate the quantum
depletion, momentum distribution and the boson contact parameter across the
resonance. The transition from condensate to molecular Fermi gas is also
discussed.Comment: 4 pages, 4 figure
Collinear antiferromagnetic state in a two-dimensional Hubbard model at half filling
In a half-filled Hubbard model on a square lattice, the next-nearest-neighbor
hopping causes spin frustration, and the collinear antiferromagnetic (CAF)
state appears as the ground state with suitable parameters. We find that there
is a metal-insulator transition in the CAF state at a critical on-site
repulsion. When the repulsion is small, the CAF state is metallic, and a van
Hove singularity can be close to the Fermi surface, resulting in either a kink
or a discontinuity in the magnetic moment. When the on-site repulsion is large,
the CAF state is a Mott insulator. A first-order transition from the CAF phase
to the antiferromagnetic phase and a second-order phase transition from the CAF
phase to the paramagnetic phase are obtained in the phase diagram at zero
temperature.Comment: 5 pages, 5 figures, two column
The induced interaction in a Fermi gas with a BEC-BCS crossover
We study the effect of the induced interaction on the superfluid transition
temperature of a Fermi gas with a BEC-BCS crossover. The
Gorkov-Melik-Barkhudarov theory about the induced interaction is extended from
the BCS side to the entire crossover, and the pairing fluctuation is treated in
the approach by Nozi\`{e}res and Schmitt-Rink. At unitarity, the induced
interaction reduces the transition temperature by about twenty percent. In the
BCS limit, the transition temperature is reduced by a factor about 2.22, as
found by Gorkov and Melik-Barkhudarov. Our result shows that the effect of the
induced interaction is important both on the BCS side and in the unitary
region.Comment: 11 pages, 3 figures, to be published in PR
Ginzburg-Landau theory of a trapped Fermi gas with a BEC-BCS crossover
The Ginzburg-Landau theory of a trapped Fermi gas with a BEC-BCS crossover is
derived by the path-integral method. In addition to the standard
Ginzburg-Landau equation, a second equation describing the total atom density
is obtained. These two coupled equations are necessary to describe both
homogeneous and inhomogeneous systems. The Ginzburg-Landau theory is valid near
the transition temperature on both sides of the crossover. In the
weakly-interacting BEC region, it is also accurate at zero temperature where
the Ginzburg-Landau equation can be mapped onto the Gross-Pitaevskii (GP)
equation. The applicability of GP equation at finite temperature is discussed.
On the BEC side, the fluctuation of the order parameter is studied and the
renormalization to the molecule coupling constant is obtained.Comment: 16 pages, 2 figures, to be published in PR
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