CAPTION: A two-layer scanning tunneling microscope (STM) image of the surface of a BSCCO (bismuth, strontium, calcium, copper and oxygen) high-temperature superconductor, showing:

(1) the atomic positions of the bismuth atoms (bottom layer) just under the surface of the superconductor;

(2) superimposed upon it the magnitude of the quantum wavefunction of the electronic "impurity state" which was discovered above the impurity atom site (a zinc atom). The electron cloud is localized around the impurity, and displays a cloverleaf shape characteristic of d-wave orbitals. Note additional diagonal bumps between the leaves of the four-leaf clover. These were not predicted by the current theory of high-temperature superconductivity.

PHOTO CREDIT: Séamus Davis/UC Berkeley

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