Yunker Lecture
Tuesday, March 2, 1999 - 16:00
Event Speaker: 
Ted Geballe, Emeritus Professor of Applied Physics and of Materials Science and Engineering, Stanford University
Local Contact: 

Magnetic materials have been known since antiquity. Many creative, romantic (but unscientific) ideas were invoked over the ensuing centuries to explain the mysterious forces of the lodestone. Not until the discoveries of quantum mechanics in the late 1920"s that it was possible to reach a scientific understanding of most magnetic metals and magnetic insulators, and then it took only a short time to do so. However there exists a class of materials, which strangely enough includes lodestone, where the electrons responsible for the magnetism cannot be described as tightly bound (as in insulators) or nearly free (as in metals) which are not well understood. Superconductivity in contrast to ancient magnetism is a discovery of the 20th century which was made almost immediately following the liquefaction of helium gas, although from what we now know it could have been discovered in the liquid nitrogen available in the previous century. Until recently magnetism and superconductivity, for well understood reasons, were found to be almost mutually exclusive. In the past decade a deep and not-yet-satisfactorily-understood relationship between the two has emerged from studies of transition metal oxides in the same regime mentioned above where the electrons cannot be described in simple local or itinerant terms, but rather are highly correlated. The major frontier of condensed matter science today is the study of materials in which the electrons are highly correlated, particularly the colossal magnetoresistance manganites and the high temperature superconducting cuprates I will give examples from ongoing intensive world wide efforts.