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High-Tc superconductivity emerges when the localized electrons of a CuO2–based antiferromagnetic Mott-insulator become itinerant due to carrier-doping. This process is not yet understood within a quantitative quantum mechanical model. We do know that the doping-induced electronic states are highly correlated and exhibit intense electron-electron interactions (antiferromagnetic exchange and unscreened coulomb forces). In addition, atomic-scale electron-lattice interactions (from Jahn-Teller effects, polaron formation and because of high iconicity of the materials) can also be intense. Which (if any) of these interactions cause the superconductivity is a mystery whose solution has eluded physicists now for 21 years. A key reason for this failure may be that almost all of these phenomena occur at high energy 50meV->100meV, are virtually local at atomic scale, and are spatially disordered because of the high dopant-atom density. No appropriate tools to determine the wavefunction structure of states emerging under these complex circumstances existed.
Here we describe the development and application of low temperature spectroscopic imaging STM (SI-STM) techniques for studies of highly correlated electronic states in transition metal oxides. They allow us to visualize the extremely complex electronic matter and interactions occurring in such systems at the atomic scale. And, as the SI-STM tools have improved, an amazingly intricate, beautiful and often counter intuitive picture of the atomic-scale electronic structure of high-Tc cuprates has emerged. Among the effects I hope to describe are the highly distinctive effects of impurity and dopant atoms, the beautiful d-wave quasiparticle interference effects, the unusual quantized vortex cores, the atomic-scale electron-lattice interactions, and the spatial self-organization of electronic structure at low hole-densities.
PI’s of this collaboration include H. Eisaki (AIST-Tsukuba), H. Takagi (RIKEN/ U. of Tokyo) and S. Uchida (U. of Tokyo).
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