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Abstract's Details

Pseudogap and Superconducting Gap —Same or Different?
Abstract IDMAT-26 
PresenterWei-Sheng  Lee
Presentation TypePoster
Full Author ListWei-Sheng Lee (1), I. M. Vishik (1), K. Tanaka (1,2), D. H. Lu (1), T. Sasagawa (1), T. P. Devereaux (3), N. Nagaosa (3), Z. Hussain (2), Z.-X. Shen (1)
Affiliations(1) Dept. of Physics, Stanford University and SSRL
(2) Advanced Light Source, Lawrence National Berkeley Lab
(3) Dept. of Physics, University of Waterloo, Canada
(4) Dept. of Physics, University of Tokyo, Japan
CategoryMaterials Science
AbstractThe superconducting gap–an energy scale tied to the superconducting phenomena-opens on the Fermi surface at the superconducting transition temperature (TCTC superconducting cuprates, a pseudogap, whose relation to the superconducting gap remains a mystery, develops well above -TC. 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. While some experimental evidence suggests they 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 Bi2Sr2 CaCu2O8+x in the momentum space region overlooked in previous measurements. Near the diagonal of Cu-O bond direction (nodal direction), we found a gap which opens at TC and exhibits a canonical (BCS-like) temperature dependence accompanied by the appearance of the so-called Bogoliubov quasiparticles, 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. We also uncover a highly non-trivial relation between the nodal region BCS gap and the pseudogap as function of temperature and doping; they develop in quite different ways, but paradoxically also appear to be intimately related as they eventually merge into an almost perfect d-wave form near optimal doping. The emerging two-gap phenomenon points to a picture of richer quantum configurations in high temperature superconductors.
Footnotes 
Funding AcknowledgementThis work is supported by DOE Office of Science, Division of Materials Science, with contract DE-FG03-01ER45929-A001 and NSF grant DMR-0604701.