Electronic structure, magnetic properties and superconductivity in the Na_xCoO₂ system

Igor Mazin

Naval Research Laboratory, 4555 Overlook Ave SW, 20375 Washington D.C., USA

I will discuss the experimental and theoretical situation regarding the electronic properties of NaxCoO2 based materials, both magnetic and (hydrated) superconducting. I will emphasize the following issues: (1) Are relevant correlations Hubbard-like ("LDA+U") or related to critical magnetic fluctuations? (2) What is the role of magnetic fluctuations in superconductivity and which superconducting symmetries are consistent with the experiment and with the theory (3) What determins the magnetic ordering in the parent compound? This work was done in collaboration with M. Johannes and D. Singh.