  A fully antisymmetrized microscopic model is developed for light two-neutron
halo nuclei using a hyper-spherical basis to describe halo regions. The
many-body wavefunction is optimized variationally. The model is applied to 6He
bound by semi realistic Minnesota nucleon-nucleon forces. The two-neutron
separation energy and the radius of the halo are reproduced in agreement with
experiment. Antisymmetrization effects between 4He and halo neutrons are found
to be crucial for binding of 6He. We also properly extract two-neutron overlap
functions and find that there is a significant increase of 30%-70% in their
normalization due to microscopic effects as compared to the results of
three-body models.
