Condensed Matter Physics Seminar

A DFT+DMFT approach to the electronic structure of the cobaltates

Dr. Chris Marianetti
Rutgers University
Tuesday, December 12, 2006
Higgins 235, 3pm

The cobaltates, NaxCoO2, have demonstrated a wide variety complex behavior.  The Na rich region of the phase diagram displays various degrees of anomalous behavior, such as Curie-Weiss behavior near a band insulator, charge disproportionation, and non-Fermi-liquid behavior in the resistivity. Alternatively, the Na poor region of the phase diagram appears to be a Fermi-liquid. The magnetic susceptibility displays Pauli behavior, the resistivity is roughly quadratic at low temperatures, and the system appears to be homogeneous. We explore the normal state of the cobaltates in the Na rich and Na poor region of the phase diagram using both density functional theory (DFT) and dynamical mean-field theory (DMFT). The Na potential is identified as a key element in generating the anomolies in the Na rich region of the phase diagram. DFT calculations indicate that the Na potential generates a binary perturbation of the Co sites, while realistic DMFT calculations for the Hubbard model in the presence of binary disorder predict Curie-Weiss behavior as observed in experiment. In the Na poor region, DFT+DMFT is used to calculate the ARPES spectrum in addition to the heat capacity. We confirm that increasing the on-site coulomb coulomb repulsion diminishes the $e_g'$ hole pockets on the Fermi surface, as observed in experiment and previous calculations.