Atomic manipulation of the gap in Bi ₂ Sr ₂ CaCu ₂ O _8+x

Manipulating the gap Cuprate superconductors typically have a large amount of spatial inhomogeneity, partly stemming from the inhomogeneity of the chemical doping process. In particular, the size of the spectroscopic gap can vary widely across a single sample. Massee et al. used the tip of a scanning tunneling microscope to manipulate atoms on the surface of a member of the Bi2Sr2CaCu2O8+x cuprate family. Moving bismuth atoms up or down caused adjacent atoms to shift laterally, leading to reversible local changes in the size of the gap. It is expected that the technique can be used to probe the influence of the local lattice on the electronic states of other correlated materials. Science, this issue p. 68 The tip of a scanning tunneling microscope is used to manipulate atoms on the surface of a cuprate, affecting the gap. Single-atom manipulation within doped correlated electron systems could help disentangle the influence of dopants, structural defects, and crystallographic characteristics on local electronic states. Unfortunately, the high diffusion barrier in these materials prevents conventional manipulation techniques. Here, we demonstrate the possibility to reversibly manipulate select sites in the optimally doped high-temperature superconductor Bi2Sr2CaCu2O8+x using the local electric field of the tip of a scanning tunneling microscope. We show that upon shifting individual Bi atoms at the surface, the spectral gap associated with superconductivity is seen to reversibly change by as much as 15 milli–electron volts (on average ~5% of the total gap size). Our toy model, which captures all observed characteristics, suggests that the electric field induces lateral movement of local pairing potentials in the CuO2 plane.