Collective excitations of a trapped boson-fermion mixture across demixing

P. CAPUZZI, A. MINGUZZI, AND M. P. TOSI

PHYSICAL REVIEW A - ATOMIC, MOLECULAR AND OPTICAL PHYSICS

Año: 2003 vol. 67 p. 53605 - 536057

1050-2947

We calculate the spectrum of low-lying collective excitations in a mesoscopic cloud formed by a Bose- Einstein condensate and a spin-polarized Fermi gas as a function of the boson-fermion repulsions. The cloud is under isotropic harmonic confinement and its dynamics is treated in the collisional regime by using the equations of generalized hydrodynamics with inclusion of surface effects. For large numbers of bosons, we find that as the cloud moves towards spatial separation demixing with increasing boson-fermion coupling, the frequencies of a set of collective modes show a softening followed by a sharp upturn. This behavior permits a clear identification of the quantum phase transition. We propose a physical interpretation for the dynamical transition point in a confined mixture, leading to a simple analytical expression for its location.