arXiv:0704.2373 · Physical Review A

Mixing-demixing transition and collapse of a vortex state in a quasi-two-dimensional boson-fermion mixture

Sadhan K. Adhikari, Luca Salasnich

Published May 8, 2007• 19 citations

Abstract

We investigate the mixing-demixing transition and the collapse in a quasi-two-dimensional degenerate boson-fermion mixture (DBFM) with a bosonic vortex. We solve numerically a quantum-hydrodynamic model based on a new density functional which accurately takes into account the dimensional crossover. It is demonstrated that with the increase of interspecies repulsion, a mixed state of DBFM could turn into a demixed state. The system collapses for interspecies attraction above a critical value which depends on the vortex quantum number. For interspecies attraction just below this critical limit there is almost complete mixing of boson and fermion components. Such mixed and demixed states of a DBFM could be experimentally realized by varying an external magnetic field near a boson-fermion Feshbach resonance, which will result in a continuous variation of interspecies interaction.

DOI: 10.1103/physreva.75.053603

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arXiv:0704.2373 · Physical Review A

Mixing-demixing transition and collapse of a vortex state in a quasi-two-dimensional boson-fermion mixture

Sadhan K. Adhikari, Luca Salasnich

Published May 8, 2007• 19 citations

arXiv HTML PDF

Abstract

DOI: 10.1103/physreva.75.053603

Related papers

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^{87}\mathrm{Rb}

and

^{40}\mathrm{K}

mixture are analyzed quantitatively. The critical number of bosons for the collapse transition is estimated without and in the presence of the vortices as a function of the fermion number. It is shown that the critical number of bosons increases in the presence of the vortex. The vortex critical velocities are calculated as functions of the numbers of bosons and fermions.

We study a dilute mixture of degenerate bosons and fermions across a Feshbach resonance of the Fermi-Fermi scattering length

{a}_{F}

. This scattering length is renormalized by the boson-induced interaction between fermions and its value is crucial to determine the phase diagram of the system. For the mixture in a box and a positive Bose-Fermi scattering length, we show that there are three possibilities: A single uniform mixed phase, a purely fermionic phase coexisting with a mixed phase, and a purely fermionic phase coexisting with a purely bosonic one. As

1∕{a}_{F}

is increased from a negative value to the Feshbach resonance

(1∕{a}_{F}=0)

, the region of pure separation increases and the other two regions are strongly reduced. Above the Feshbach resonance

(1∕{a}_{F}>0)

, pairs of Fermi atoms become Bose-condensed molecules. We find that these molecules are fully spatially separated from the bosonic atoms when

1∕{a}_{F}

exceeds a critical value. For a negative Bose-Fermi scattering length we deduce the condition for collapse, which coincides with the onset of dynamical instability of the fully mixed phase. We consider also the mixture in a harmonic trap and determine the conditions for partial demixing, full demixing, and collapse. The experimental implications of our results are investigated by analyzing mixtures of $^{6}\mathrm{Li}\text{\ensuremath{-}}^{23}\mathrm{Na}$ and $^{40}\mathrm{K}\text{\ensuremath{-}}^{87}\mathrm{Rb}$ atoms.