Thomas Lee Elifritz

http://www.nature.com/nphys/journal/vaop/ncurrent/abs/nphys2321.html

Visualization of the emergence of the pseudogap state and the evolution to superconductivity in a lightly hole-doped Mott insulator, Y. Kohsaka, T. Hanaguri, M. Azuma, M. Takano, J. C. Davis and H. Takagi, Nature Physics, Published Online 20 May 2012.

Superconductivity emerges from the cuprate antiferromagnetic Mott state with hole doping. The resulting electronic structure is not understood, although changes in the state of oxygen atoms seem paramount. Hole doping first destroys the Mott state, yielding a weak insulator, where electrons localize only at low temperatures without a full energy gap. At higher doping levels, the ‘pseudogap’, a weakly conducting state with an anisotropic energy gap and intra-unit-cell breaking of 90° rotational (C_4v) symmetry, appears. However, a direct visualization of the emergence of these phenomena with increasing hole density has never been achieved. Here we report atomic-scale imaging of electronic structure evolution from the weak insulator through the emergence of the pseudogap to the superconducting state in Ca_2−xNa_xCuO₂Cl₂. The spectral signature of the pseudogap emerges at the lowest doping level from a weakly insulating but C_4v-symmetric matrix exhibiting a distinct spectral shape. At slightly higher hole density, nanoscale regions exhibiting pseudogap spectra and 180° rotational (C_2v) symmetry form unidirectional clusters within the C_4v-symmetric matrix. Thus, hole doping proceeds by the appearance of nanoscale clusters of localized holes within which the broken-symmetry pseudogap state is stabilized. A fundamentally two-component electronic structure11 then exists in Ca_2−xNa_xCuO₂Cl₂ until the C_2v-symmetric clusters touch at higher doping levels, and the long-range superconductivity appears.

Ok, I guess that, as they say, is that.

Parts is parts!

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