## Abstract

The essential framework for cuprate superconductivity is that of a spin-1/2 electron system in the vicinity of a half filled (Mott limit) lattice. Of all oxide superconductors, this framework is most closely matched in the sodium doped cobalt oxides except that it is realized on a triangular lattice. We employ angle-resolved photoemission spectroscopy to study the quasiparticle dynamics of the parent cobaltate superconductor. Results reveal a single hole-like Fermi surface generated by the crossing of heavy (∼15 m_{e} ∼ 3m_{LDA}) quasiparticles with a negative effective hopping (t_{eff} < 0). The observed ground state as given by the topology of the Fermi surface is found be very close to a collective charge instability with sqrt(3) × sqrt(3) symmetry. The measured electron dynamic parameters reveal the unusual character of the parent cobaltate class likely due to small and almost isotropic Fermi velocity (v_{F} (over(k, →)) ∼ v_{F} ∼ 0.4 ± 0.1 eV Å) observed. ARPES data is consistent with bulk thermodynamic specific heat and quantum oscillation measurements.

Original language | English (US) |
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Pages (from-to) | 186-189 |

Number of pages | 4 |

Journal | Physica C: Superconductivity and its applications |

Volume | 460-462 I |

Issue number | SPEC. ISS. |

DOIs | |

State | Published - Sep 1 2007 |

## All Science Journal Classification (ASJC) codes

- Electronic, Optical and Magnetic Materials
- Condensed Matter Physics
- Energy Engineering and Power Technology
- Electrical and Electronic Engineering

## Keywords

- Doped Mott insulators
- Photoemission spectroscopy
- Sodium cobaltates
- Superconductivity