Years have elapsed without a consensus on the full microscopic understanding of the physics involved in cuprate superconductors. One problem central to experimentalists is the residence of doped holes. Although widely held that at low concentrations of dopants, most holes go to Zhang-Rice orbital, whose character is essentially of planar O p orbital, what happens in the overdoped case is still not clear. In this Science report [1], the workers used high resolution Compton scattering to resolve this issue. They claimed that, doped holes are mostly of Cu d character in the OD case. Their results resonate with a two-orbital model [2] that takes into account both dz^2 and dx^2-y^2 orbital. In ref.[2], the energy difference between these orbital, Delta, is the key parameter in determining Tc. Larger Delta gives larger Tc. What is implied in [1], is perhaps that, such Delta should depend on doping x. As x increases, Delta decreases. This might explain the fact that, the SC dome has a small collapse at its up right corner.
Is there a sharp transition ?
[1]Science, 332:698(2011)
[2]PRL, 105:057003(2010)
I would like to mention another paper, which measures orbital current in CuO[Science, 332:696(2011)].
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