Local Ordering in the Pseudogap State of the High-T$_c$ Superconductor   Bi$_2$Sr$_2$CaCu$_2$O$_{8+\delta}$
  We report atomic scale characterization of the pseudogap state in a high-T$_c$ superconductor, Bi$_2$Sr$_2$CaCu$_2$O$_{8+\delta}$. The electronic states at low energies within the pseudogap exhibit spatial modulations having an energy-independent incommensurate periodicity. These patterns, which are oriented along the copper-oxygen bond directions, appear to be a consequence of an electronic ordering phenomenon--the observation of which correlates with the pseudogap in the density of electronic states. Our results provide a stringent test for various ordering scenarios in the cuprates, which have been central in the debate on the nature of the pseudogap and the complex electronic phase diagram of these compounds. 
Michael Vershinin (1), Shashank Misra (1), S. Ono (2), Y. Abe (2),   Yoichi Ando (2), and Ali Yazdani (1) ((1) University of...