US-Germany Cooperative Research: Theory of Grain Boundaries and Surfaces of High Temperature Superconductors

University Of Florida, Gainesville FL

Investigators

Abstract

0340536 Hirschfeld This award supports Peter Hirschfeld and students from the University Florida in a collaboration with Thilo Kopp of the Department of Physics at the University of Augsburg, Germany and Yuri Barash of the Moscow Institute of Physics and Technology in Russia. The collaboration will investigate a series of problems related to surface properties of d-wave superconductors relevant to cuprate and other novel materials displaying unconventional superconductivity. The scientific problems include the modeling of grain boundaries in correlated (normal and superconducting) systems to predict transport properties and extract information regarding unconventional superconducting and magnetic order parameter symmetry. In recent years it has become clear that other ordered states besides d-wave superconductivity are relatively low in energy, and may manifest themselves when the d-wave order is suppressed, e.g., at surfaces, grain boundaries, or regions of disorder. Nanoscale inhomogeneity in electronic structure has recently been observed in the BSCCO-2212 system, and there is some evidence that this disorder may not only be intrinsic, but may provide an important clue to the origin of high-Tc superconductivity. Phenomenological studies of surfaces and grains will aid in understanding the origin of these nanoscale structures. Broader impact of the proposal There are enormous practical implications for superconducting microwave and power applications if the grain boundary problem can be solved. At present the effect limiting the critical current Jc in wires and tapes appears to be the presence of grain boundaries in all samples. It is not currently understood at a fundamental level why there is an exponential suppression of Jc with the misorientation angle between grains, but it is clear that the d-wave symmetry of the order parameter is a crucial factor. Simple phenomenological pictures are known to fail, and if the proposed investigations can provide an answer, this important obstacle to applications will be overcome. The broader impact of the proposal also includes the educational benefits to the US graduate students, who will be trained in an international setting in methods pertaining to these problems. Benefits to a wider community will accrue in the sense that many of the ideas discussed also pertain to several classes of novel superconductors under intense scientific scrutiny, including the organic superconductors, ruthenates, heavy fermions and borocarbides. Results will be disseminated through publications, the PI's web site, and seminars at the University of Florida and elsewhere.