Intrinsic Gap and Exciton Condensation in the ν_T=1 Bilayer System

We investigate the quasiparticle excitation of the bilayer quantum Hall (QH) system at a total filling factor ν_T=1 in the limit of negligible interlayer tunneling under a tilted magnetic field. We show that the intrinsic quasiparticle excitation is of purely pseudospin origin and solely governed by the inter- and intralayer electron interactions. A model based on exciton formation successfully explains the quantitative behavior of the quasiparticle excitation gap, demonstrating the existence of a link between the excitonic QH state and the composite fermion liquid. Our results provide a new insight into the nature of the phase transition between the two states.