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Published June 2, 2006 | Published
Journal Article Open

Low-Lying Quasiparticle States and Hidden Collective Charge Instabilities in Parent Cobaltate Superconductors

Abstract

We report a state-of-the-art photoemission (angle-resolved photoemission spectroscopy) study of high quality single crystals of the Na_xCoO_2 series focusing on the fine details of the low-energy states. The Fermi velocity is found to be small (<0.5   eV    Å) and only weakly anisotropic over the Fermi surface at all dopings, setting the size of the pair wave function to be on the order of 10–20 nm. In the low-doping regime, the exchange interlayer splitting vanishes and two-dimensional collective instabilities such as 120°-type fluctuations become kinematically allowed. Our results suggest that the unusually small Fermi velocity and the unique symmetry of kinematic instabilities distinguish cobaltates from most other oxide superconductors.

Additional Information

© 2006 The American Physical Society. Received 27 December 2005. Published 1 June 2006. We gratefully acknowledge P.W. Anderson, D. A. Huse, S. A. Kivelson, P. A. Lee, N. P. Ong, S. Shastry, and S. Sondhi for discussions. This work is partially supported through the NSFMRSEC (DMR-0213706), DOE Grants No. DE-FG02-05ER46200 and No. DE-FG02-98-ER45706, and NSFC (Grant No. 10574158). ALS is supported by DOE/BES-DEAC03-76SF00098.

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Published - PhysRevLett.96.216405.pdf

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August 19, 2023
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