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Nanoscale Imaging Reveals Local Superconductivity Above Tc

Using a specially-designed scanning tunneling microscope, PCCM researchers have mapped the strength of current-carrying electron pairs as they form in a ceramic high-temperature superconductor. From the top left, the images show the same 30 nm x 30 nm region of the material at successively lower temperatures spanning T<sub>c</sub>, the temperature at which the entire sample exhibits superconductivity, . Red areas indicate the presence of superconducting pairs. Even at 10<sup>o</sup>C above T<sub>c</sub> (top left image), the electron pairs still exist in localized regions.
Superconductivity, the ability to carry electrical current without resistance, would revolutionize power transmission if the property appeared in a material at close to room temperature. Two decades ago a class of materials, the copper oxides, were discovered to show superconductivity at temperatures up to 140 degrees below room temperature . The mechanism of superconductivity and possible methods to enhance it has remained one of the biggest challenges in condensed matter physics. Using a new experimental technique to directly visualize the formation of superconductivity at the nanoscale, the Princeton team has discovered that traces of superconductivity remain present inside copper oxides even when they are warmed up above the critical temperature where they lose their resistance. Though the entire sample is too warm to exhibit superconductivity, disconnected nanoscale regions within it possess Cooper pairs -- the coupled electrons that carry current through a superconductor. The pairing appears to persist to temperatures as much as 50 degrees higher than the critical temperature. These measurements demonstrate that the pairing mechanism is local in nature and is a strong function of the heterogeneous material chemistry of the copper oxides on the atomic scale.