Suppression of Superfluid Density and the Pseudogap State in the   Cuprates by Impurities
  We use scanning tunneling microscopy (STM) to study magnetic Fe impurities intentionally doped into the high-temperature superconductor Bi$_{2}$Sr$_{2}$Ca$_{2}$CuO$_{8+\delta}$. Our spectroscopic measurements reveal that Fe impurities introduce low-lying resonances in the density of states at \Omega$_{1}$ $\approx$ 4meV and \Omega$_{2}$ $\approx$ 15 meV allowing us to determine that, despite having a large magnetic moment, potential scattering of quasiparticles by Fe impurities dominates magnetic scattering. In addition, using high-resolution spatial characterizations of the local density of states near and away from Fe impurities, we detail the spatial extent of impurity affected regions as well as provide a local view of impurity-induced effects on the superconducting and pseudogap states. Our studies of Fe impurities, when combined with a reinterpretation of earlier STM work in the context of a two-gap scenario, allow us to present a unified view of the atomic-scale effects of elemental impurities on the pseudogap and superconducting states in hole-doped cuprates; this may help resolve a previously assumed dichotomy between the effects of magnetic and non-magnetic impurities in these materials. 
Unurbat Erdenemunkh, Brian Koopman, Ling Fu, Kamalesh Chatterjee, W.   D. Wise, G. D. Gu, E. W. Hudson, Michael C. Boyer
cond-mat.supr-con