Structure of a quantized vortex in boson systems

Jian‐Ming Tang

Masahiko Machida, Tomio Koyama

In atomic Fermi gases, the pairing character changes from BCS‐like to BEC‐like when one decreases the threshold energy of the Feshbach resonance. With this crossover, the system enters the strong‐coupling regime through the population enhancement of diatom molecules, and the vortex structure becomes much different from well‐known core structures in BCS superfluid since the superfluid order parameter is given by a sum of BCS pairs and BEC molecular condensates. In this paper, we study the structure of a vortex by numerically solving the generalized Bogoliubov‐de Gennes equation derived from the fermion‐boson model and clarify how the vortex structure changes with the threshold energy of the Feshbach resonance. We find that the diatom boson condensate enhances the matter density depletion inside the vortex core and the discreteness of localized quasi‐particle spectrum.

Masahiko Machida, Yoji Ohashi, T. Koyama

In order to understand what kind of information can be extracted from the vortex-core structure in superfluid fermion-atom gases we make a systematic study for the core structure of a singly quantized vortex in the range of broad Feshbach resonance, solving numerically the generalized Bogoliubov--de Gennes equation derived from the fermion-boson model. Numerical calculations reveal that the vortex core can be well characterized by three length scales from the spatial variation of the fermionic and bosonic gap functions. We also predict that the profile of matter depletion and the quasiparticle spectrum show distinctive differences between the BCS and Bose-Einstein Condensate regimes.

Lara Thompson, Philip C. E. Stamp

J. Horne, Jorge A. Salas, Kálmán Varga

Masahiko Machida, T. Koyama

In order to clarify the structure of a singly quantized vortex in a superfluid fermion gas near the Feshbach resonance, we numerically solve the generalized Bogoliubov-de Gennes equation in the boson-fermion model. The superfluid gap, which contains contributions from both condensed fermion pairs and condensed bosons, is self-consistently determined, and the quasiparticle excitation levels bound in the vortex core are explicitly shown. We find that the boson condensate contributes to enhance the matter density depletion and the discreteness of localized quasiparticle spectrum inside the core. It is predicted that the matter density depletion and the discrete core levels are detectable in the vicinity of the BCS-Bose-Einstein condensation crossover point.