A well-established trend in cuprate high temperature superconductors is that for each homologous series the maximum Tc increases with the number of CuO2 planes per unit cell up to the trilayer limit. Trilayer cuprates not only have the highest Tc, but also have the unique situation with two types of inequivalent CuO2 planes. In this talk, we present STM studies of the atomic scale electronic structure of Bi2Sr2Ca2Cu3O10+δ (Bi-2223) trilayer cuprates with varied dopings. We find that most tunneling spectra exhibit two superconducting gaps, presumably from the inner and outer CuO2 planes respectively. The superconducting properties show spatial variations that are correlated with the structural supermodulation, and the effect is much more pronounced in the underdoped regime. The two superconducting gaps both decrease rapidly with increasing doping, despite the nearly constant Tc in the overdoped regime. There is an absence of quasiparticle interference in the antinodal region of strongly overdoped Bi-2223, but instead an electronic order with periodicity starts to emerge. More remarkably, this order also breaks the particle-hole symmetry, resulting in two asymmetric SC coherence peaks that alternate periodically in space. We propose that the key underlying physics for these anomalous observations is the intricate interaction between the two types of CuO2 planes in Bi-2223, which leads to unique band dispersion of the Bogoliubov quasiparticles, especially in the antinodal regime.
Yayu Wang received his B.S. degree in physics from the University of Science and Technology of China in 1998 and his Ph.D. from Princeton University in 2004. From 2004 and 2007 he was a Miller research fellow at UC Berkeley. After a brief visit to MIT, he joined the physics department of Tsinghua University in December 2007. His recent research interests include transport studies of topological insulators and STM studies of high temperature superconductors.
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