Materials World Network: Interfacial Phenomena in Superconducting Heterostructures

University Of Minnesota-Twin Cities, Minneapolis MN

Investigators

Abstract

The objectives of this research are to synthesize, characterize, and study experimentally and theoretically properties associated with interfacial phenomena in epitaxial heterostructures consisting of complex oxide superconductors (cuprates), and ferromagnets (manganites) and oxide superconductors incorporated into field effect structures with oxide gate insulators. This effort combines the techniques developed by the Spanish investigator (Jacobo Santamaria, Universidad Complutense, Madrid) for the fabrication of epitaxial films of oxides using relatively simple high-pressure oxygen sputtering techniques, with the theoretical and experimental capabilities of the US investigators at Minnesota (Allen Goldman) and Georgia Tech (Carlos Sa de Melo) and their collaborators at Argonne (Suzanne ter Velthuis) and Oak Ridge National Laboratories (Maria Varela). The unifying concepts of this effort are the use of spin from an oxide ferromagnet and induced charge from a field effect gate to study the ground state and excited states of high temperature superconducting films. There are two main research themes: (1) Spin injection and related phenomena in complex oxide superconducting/ferromagnetic heterostructures and (2) charge effects and quantum order in complex oxide superconducting nano- films. The effects of spin injection on the quasiparticles and the condensate of cuprate films and the roles of Andreev reflections and the magnetic proximity effect on the spin relaxation time and length in cuprate films are examined. The possibilities of inducing exotic pairing states in ferromagnetic oxides and using the field effect to tune the properties of an "under doped" cuprate in the pseudogap phase into the superconducting state are also explored. A goal of the latter effort is to investigate the use of field effect doping to determine whether the zero-temperature end point of the boundary between the pseudogap and the superconducting phases is a quantum critical point connecting two different superconducting ground states. The experimental tools used to address these issues include electron tunneling and electrical transport, and with collaborators at Oak Ridge and Argonne National Laboratories, electron microscopy and neutron scattering. The theoretical tools used involve many body techniques that parallel and complement the experimental investigations. This international effort allows for strong interaction of students and postdoctoral associates from the US and Spain, which broadens the experience of young scientists in the global scientific community. This award is co-funded with the Office of International Science and Engineering.