Regensburg 2007 – scientific programme

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TT: Fachverband Tiefe Temperaturen

TT 13: Symposium “Superconductivity and Magnetism in Lamellar Cobaltates”

TT 13.1: Invited Talk

Tuesday, March 27, 2007, 14:00–14:30, H18

Angle-resolved photoemission studies on Na_xCoO₂ — •Hong Ding — Boston College, Chestnut Hill, MA, USA

In this talk I will report a systematic angle-resolved photoemission study of Na_xCoO₂ single crystals for a wide range of Na concentrations. We observed a large Fermi surface centered at the Γ point, which satisfies Luttinger counting theorem when x < 0.75. The small Fermi surface pockets predicted by LDA band calculations near the K points are not observed. Instead, "sinking islands" with the binding energy of 50 - 200 meV are observed. All of these, along with a large band renormalization, may be caused by the strong correlations in this material. In addition, at x = 1/3 where superconductivity occurs with proper water intercalation, we found that the large Fermi surface coincides with the new zone boundary of a commensurate charge ordering, suggesting that the charge fluctuations may play an important role in the superconductivity of this material.