A Gulf Between Two Gaps

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Science  22 Dec 2006:
Vol. 314, Issue 5807, pp. 1837e
DOI: 10.1126/science.314.5807.1837e

In the high-temperature superconductors, the onset of superconductivity is preceded by a region known as the pseudogap, particularly in underdoped samples. The relation of the pseudogap to superconductivity has been controversial, in part because different experiments have generated conflicting results. With improvements in sample quality and using an optimized, angle-resolved photoemission spectroscopy technique, Tanaka et al. (p. 1910, published online 16 November) reveal the presence of two gaps with different doping dependence, one gap with the pseudogap and the other with the superconducting gap. Valla et al. (p. 1914, published online 16 November) present results of a photoemission and scanning tunneling microscopy study on a nonsuperconducting cuprate that still exhibits the d-wave signature of its superconducting cousins. The results suggest that the pseudogap regime is formed as electrons pair up, but without the global coherence associated with the superconducting state. These results, which suggest that the pseudogap and superconducting gap coexist but are not related, should have implications for understanding superconductivity mechanisms (see the Perspective by Millis and the 17 November news story by Service).


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