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- Title
Abrupt onset of a second energy gap at the superconducting transition of underdoped Bi2212.
- Authors
Lee, W. S.; Vishik, I. M.; Tanaka, K.; Lu, D. H.; Sasagawa, T.; Nagaosa, N.; Devereaux, T. P.; Hussain, Z.; Shen, Z.-X.
- Abstract
The superconducting gap—an energy scale tied to the superconducting phenomena—opens on the Fermi surface at the superconducting transition temperature (Tc) in conventional BCS superconductors. In underdoped high-Tc superconducting copper oxides, a pseudogap (whose relation to the superconducting gap remains a mystery) develops well above Tc (refs 1, 2). Whether the pseudogap is a distinct phenomenon or the incoherent continuation of the superconducting gap above Tc is one of the central questions in high-Tc research. Although some experimental evidence suggests that the two gaps are distinct, this issue is still under intense debate. A crucial piece of evidence to firmly establish this two-gap picture is still missing: a direct and unambiguous observation of a single-particle gap tied to the superconducting transition as function of temperature. Here we report the discovery of such an energy gap in underdoped Bi2Sr2CaCu2O8+δ in the momentum space region overlooked in previous measurements. Near the diagonal of Cu–O bond direction (nodal direction), we found a gap that opens at Tc and has a canonical (BCS-like) temperature dependence accompanied by the appearance of the so-called Bogoliubov quasi-particles, a classical signature of superconductivity. This is in sharp contrast to the pseudogap near the Cu–O bond direction (antinodal region) measured in earlier experiments.
- Subjects
BAND gaps; COPPER compounds; COPPER oxide superconductors; SUPERCONDUCTIVITY; ENERGY-band theory of solids; ELECTRIC conductivity; QUASIPARTICLES; NUCLEAR particle research; SUPERCONDUCTORS
- Publication
Nature, 2007, Vol 450, Issue 7166, p81
- ISSN
0028-0836
- Publication type
Article
- DOI
10.1038/nature06219