Abstract: I will describe our studies of the high-Tc superconductor
BiSrCaCuO, using a high resolution very low temperature STM, in which single
impurity atoms are used to probe the structure of the order parameter and
the correlation between electrons.
Quasiparticle scattering at impurities generates localized "impurity
states" at the atomic scale[1]. Imaging of the impurity states associated
with individual (non-magnetic) Zn dopant atoms[2] substituted at the Cu site
in the CuO2 plane of BSCCO shows several direct real-space consequences of
the d-wave nature of the order parameter. The spectra are in qualitative
agreement with d-wave BCS theories of non-magnetic quasiparticle scattering
at a single impurity atom [3]. The destruction of superconductivity within
1.5 nm of the Zn sites is observed.
I will also discuss very new results of imaging of the impurity states
associated with individual Ni dopant atoms (magnetic) substituted at the Cu
site, which show numerous new atomic-scale phenomena which, although
partially consistent with theory for magnetic impurity atom scattering in a
d-wave BCS context, are not fully described by existing theories.
[1] Science 285, 88 (1999).
[2] Nature 403, 746 (2000).
[3] M. Salkola,A. Balatsky, D. Scalapino, Phys Rev. Lett. 77, 1841 (1996).