Ground State of v=1 Bilayer Quantum Hall Systems
  The ground-state wave function and the energy gap are calculated for various layer separations d and for up to 24 electrons by the density matrix renormalization group (DMRG) method. Two-particle distribution function and excitonic correlation function are calculated from the ground-state wave function, and the evolution of the ground state with increasing d is analyzed. The results indicate that the transition is continuous. A smooth crossover of the ground state is found at around d/l ~ 1.6 from the excitonic character at small d/l to the independent Fermi-liquid character at large d/l, where l is the magnetic length. 
Naokazu Shibata and Daijiro Yoshioka