  With the classical three-dimensional ensemble model, we have investigated the
microscopic recollision dynamics in nonsequential double ionization of helium
by 800 nm laser pulses at 2.0 PW/cm^2. We demonstrate that the asymmetric
energy sharing between the two electrons at recollision plays a decisive role
in forming the experimentally observed V-shaped structure in the correlated
longitudinal electron momentum spectrum at the high laser intensity [Phys. Rev.
Lett. 99, 263003 (2007)]. This asymmetric energy sharing recollision leaves
footprints on the transverse electron momentum spectra, which provide a new
insight into the attosecond three-body interactions.
