Doubling of the Bands in Overdoped Bi2Sr2CaCu2O

We present high resolution angle resolved photoemission data of the bilayer superconductor Bi2Sr 2CaCu2O8+δ (Bi2212) showing a clear doubling of the near EF bands. This splitting approaches zero along the (0,0)→(π,π) nodal line and is not observed in single layer Bi2Sr 2CuO 6+δ (Bi2201), indicating that the splitting is due to the long sought after bilayer splitting effect. The splitting has a magnitude of approximately 75 meV near the middle of the zone, extrapolating to about 110 meV near the (π,0) point. The existence of these two bands also helps to clear up the recent controversy concerning the topology of the Fermi surface