Structure and stability of quasi-two-dimensional boson–fermion mixtures with vortex–antivortex superposed states

Abstract

We investigate the equilibrium properties of a quasi-two-dimensional degenerate boson–fermion mixture (DBFM) with a bosonic vortex–antivortex superposed state (VAVSS) using a quantum-hydrodynamic model. We show that, depending on the choice of parameters, the DBFM with a VAVSS can exhibit rich phase structures. For a repulsive boson–fermion (BF) interaction, the Bose–Einstein condensate may constitute a petal-shaped ‘core’ inside the honeycomb-like fermionic component, or a ring-shaped joint ‘shell’ around the onion-like fermionic cloud, or multiple segregated ‘islands’ embedded in the disc-shaped Fermi gas. For an attractive BF interaction just below the threshold for collapse, an almost complete mixing between the bosonic and fermionic components is formed, where the fermionic component tends to mimic a bosonic VAVSS. The influence of an anharmonic trap on the density distributions of the DBFM with a bosonic VAVSS is discussed. In addition, a stability region for different cases of the DBFM (without vortex, with a bosonic vortex and with a bosonic VAVSS) with specific parameters is given.