SU(4) skyrmions and activation energy anomaly in bilayer quantum Hall systems

The SU(4) isospin coherence develops spontaneously in the v = 1 bilayer QH system, where quasiparticles are SU(4) skyrmions. If the tunneling gap is not too large, only pseudospins are excited at the balanced point. It evolves continuously from the pseudospin-skyrmion limit into the spin-skyrmion limit as the system is transformed from the balanced point to the monolayer point by controlling the bias voltage. Our theoretical result explains quite well the experimental data due to Murphy et al. and Terasawa et al. on the activation energy anomaly induced by applying parallel magnetic field.