STM Studies of Near-Optimal Doped Bi$_2$Sr$_2$CaCu$_2$O$_{8+\delta}$
  In this paper we summarize our STM studies of the density of electronic states in nearly optimally doped Bi$_2$Sr$_2$CaCu$_2$O$_{8+\delta}$ in zero field. We report on the inhomogeneity of the gap structure, density of states modulations with four-lattice constant period, and coherence peak modulation. 
A. Kapitulnik, A. Fang, C. Howald, and M. Greven