Local Ordering in the Pseudogap State of the High-Tc

We report atomic-scale characterization of the pseudogap state in a high-Tc superconductor, Bi2Sr2CaCu2O8. The electronic states at low energies within the pseudogap exhibit spatial modulations having an energy-independent in-commensurate periodicity. These patterns, which are oriented along the cop-per-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. Adding charge carriers to antiferromagnetic Mott insulators produces some of the most fascinating and unconventional electronic states of matter. In cuprates, samples with low hole concentration exhibit, in addition t