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Scanning tunneling microscopy (STM) has revealed numerous manifestations of nanoscale electronic disorder in the high-Tc superconductor Bi2Sr2CaCu2O8+δ. The superconducting energy gap magnitude is found to vary by up to a factor of four over nanometer length scales for all dopings1. Additionally, interference effects due to scattering of quasiparticles are found throughout all samples although no obvious scattering sites are present2. Finally, the low-bias topography shows long wavelength disorder which has been thought to imply nanoscale charge density variations3. Randomness in dopant-atom distributions has long been suspected as a possible cause for such atomic-scale electronic disorder in cuprates, but it was impossible to test this conjecture directly. Here I will introduce new techniques allowing the first simultaneous imaging of dopant atom locations and atomic-scale electronic structure in a cuprate superconductor. They reveal directly how the dopant atoms (a) strongly influence all types of electronic disorder - principally by shifting spectral weight from low to high energy nearby, (b) do not produce significant charge density fluctuations, and (c) are the primary scattering centers associated with both quasiparticle interference effects and superconducting coherence peak suppression4. I will refer to recent theoretical advances5 in discussing new insights into the nature of high Tc superconductivity which can be drawn from these STM observations.
This work was in collaboration with K. McElroy(LBNL), Jinho Lee(Cornell), J. A. Slezak(Cornell), D.-H. Lee(Berkeley), H. Eisaki(Tsukuba) & S. Uchida (Tokyo). 1 Lang et al Nature 415, 412 (2002) ; McElroy et al cond-mat/0406491. 2 McElroy et al Nature 422, 520 (2003). 3 Z. Wang et al., Phys. Rev. B 65, 064509 (2002); Q.-H. Wang, et al Phys. Rev. B 65, 054501 (2002); I. Martin & A. V. Balatsky, Physica C Superconductivity 357, 46 (2001). 4 K. McElroy et al, Submitted (2005). 5 Nunner, Andersen, Melikyan & Hirschfeld, Submitted (2005). |