Noisy defects in a doped Mott insulator*

Detailed studies of the effect of single dopant atoms on the local electronic properties are crucial for a full understanding of the macroscopic characteristics of host materials ranging from semiconductors to high temperature superconductors. Due to limited time resolution of conventional scanning tunnelling microscopes, most atomic scale studies of the latter systems focussed on the time averaged effect of dopants on the electronic structure. I will present how, by using atomic scale shot-noise measurements in the high temperature superconductor Bi2Sr2CaCu2O8+x, we visualize sub-nanometre sized objects where remarkable dynamics leads to an enhancement of the tunnelling current noise by at least an order of magnitude. From the position, current and energy dependence we deduce that these defects are oxygen dopant atoms whose local environment leads to charge dynamics that strongly affect the tunnelling mechanism. Possible effects on superconductivity will be discussed.