Positron-atom complexes as quantum halo states

The wave functions of a number of positron-atom complexes are analyzed and three of the systems, namely, e+Be, e+Na, and e +He(3Se), are seen to exhibit quantum halo structures with 45%-50% of their probability distribution lying in the large r classically forbidden region. The mean square distance between the large r fragments (e+ + Be, Ps + Na+, Ps + He+) for these systems range from 1.8 to 2.2 times larger than the square of the classical turning point, another indication of their halolike nature. � 2005 The American Physical Society.