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
(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).