An improved composite-boson theory of quantum Hall ferromagnets is for
mulated both for the monolayer and bilayer systems. In this scheme the
field operator describes solely the physical degrees of freedom repre
senting the deviation from the ground state. Skyrmions are charged exc
itations confined to the lowest Landau level. By evaluating the excita
tion energy of one skyrmion in the interlayer-coherent phase it is sho
wn that the bilayer QH state becomes stabler as the interlayer density
difference becomes larger. (C) 1998 Elsevier Science B.V.