Doubly Enhanced Skyrmions in $\nu =2$ Bilayer Quantum Hall States
  By tilting the samples in the magnetic field, we measured and compared the Skyrmion excitations in the bilayer quantum Hall (QH) state at the Landau-level filling factor $\nu =2$ and in the monolayer QH state at $\nu =1$. The observed number of flipped spins is $N_s=14$ in the bilayer system with a large tunneling gap, and $N_s=7$ in the bilayer system with a small tunneling gap, while it is $N_s=7$ in the monolayer system. The difference is interpreted due to the interlayer exchange interaction. Moreover, we have observed seemingly preferred numbers $N_s=14,7,1$ for the flipped spins by tilting bilayer samples. 
N. Kumada (1), A. Sawada (1), Z. F. Ezawa (1), S. Nagahama (1), H.   Azuhata (1), K. Muraki (2), T. Saku (2) and Y. Hirayama...