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Scientific Highlight
Shen Lab


30 January 2007

  Minding the Gaps: Explaining the Behavior of a High-Temperature Superconductor

summary written by Alison Drain, SLAC Communication Office


Scientists at Stanford University have recently made an important discovery about the coexistence of two distinct energy gaps in photoemission spectra of high temperature superconductors. The two gaps have opposite doping dependence, which provides an explanation for the contradictory results about the superconducting gap deduced from different experimental techniques. The findings, published in the December 22 issue of Science, have profound implications for the mechanism of high temperature superconductivity.

The researchers studied the effects of changes in doping level on the evolution of the electronic structure in the highly underdoped cuprate superconductor Bi2Sr2Ca1-xYxCu2O8+d (Bi2212), using powerful angle-resolved photoemission spectroscopy (ARPES). Significantly improved crystal quality, along with the state-of-the-art experimental system at SSRL beam line 5-4 allowed the scientists to address the "pseudogap and superconducting gap" issue in a depth that had not be reached by previous ARPES measurements.

Based on their experimental observations of two coexisting energy gaps, the group, led by Professor Zhi-Xun Shen, proposed a scenario with two important implications. First, the pseudogap state in the deeply underdoped samples probably competes with the superconducting state rather than preceding it, as previously suggested. Second, the data suggest that the weakened superconductivity in the underdoped regime arises not only from the loss of phase coherence but also from the weakening of electron pairing amplitude because of competing states. The implications of these findings could lead to a microscopic theory of high-temperature superconductivity.

To learn more about this research see the full scientific highlight at:

Kiyohisa Tanaka, W. S. Lee, D. H. Lu, A. Fujimori, T. Fujii, Risdiana, I. Terasaki, D. J. Scalapino, T. P. Devereaux, Z. Hussain, Z.-X. Shen, Science 314, 1910 (2006).