Condensed Matter Seminar

Probing Hybridization: Understanding the Many Faces of Magnetism

Kenneth S. Burch
Center for Integrated Nanotechnologies
Los Alamos National Laboratory

Friday, October 13, 2006 - 4:00 P.M., NSH 184

In this talk I will outline our recent optical studies to understand the effects of hybridization between local moments and free carriers on the bandstructure and ground states of dilute magnetic semiconductors and heavy Fermion superconductors. I will begin with by detailing our recent work on as grown and annealed thin films of Ga_1-xMn_xAs across its phase diagram. We find that the spectra significantly differ from what is expected and has been observed in semiconductors doped with non-magnetic impurities. These studies indicate that the Insulator to Metal transition in this magnetic semiconductor is significantly different from most other doped semiconductors, indicating an important role for magnetism. I will then switch to discussing the 1-1-5 series of heavy Fermion superconductors. We find strong deviations of the spectra from the predictions of the periodic Anderson model, which we can explain by accounting for the momentum dependence of the hybridization between the local moments and the conducting carriers. Furthermore we find correlations between the hybridization strength on a particular band and some properties of the 1-1-5 compounds, suggesting that the momentum dependence of hybridization plays a critical role in understanding the underlying physics of these heavy Fermion superconductors.