Chalcogenides Superconductors: Nonconventional Superconductivity in New Phases

Florida State University, Tallahassee FL

Investigators

Abstract

Non-Technical Abstract Superconductivity is a quantum phenomenon in which, below a critical temperature, the electrical resistance completely vanishes. Conventional superconductors, discovered over 100 years ago, are composed of simple metals, and the phenomenon was completely explained about 50 years ago. The applications of superconductors include the ability to transmit many times more power than metals at the same temperature and cross-sectional area. However, conventional superconductors are limited in that they have to be cooled to very low temperatures. More importantly, they are limited in the magnitude of current they can transmit (critical current) in an external magnetic field (critical field). Over the years, conventional superconductors have been improved and new areas have been discovered that enhanced these current carrying capabilities in a magnetic field, making possible high-field research magnets and applications that include MRI (Magnetic Resonance Imaging). Enter the discoveries of unconventional superconductors about 40 years ago, followed by the discovery of high-temperature superconductors 30 years ago, these materials which are not good metals above their critical temperature, are not completely understood, but many of these intriguing materials can transmit much more current in extremely high magnetic fields than conventional superconductors. Not only can the applications of unconventional superconductors be transformative, but the fundamental physics explaining their normal and superconducting properties remains elusive over all of this time. With the support of the Solid State and Materials Chemistry program, the research group will study unconventional superconductor phases that include metals such as niobium and tantalum, as well as the nonmetallic elements sulfur, selenium or tellurium. Technical Abstract Transition metal chalcogenides comprise superconducting phases with high critical temperatures, such as iron and molybdenum chalcogenides. The research effort focuses on new ternary and quaternary niobium and tantalum chalcogenides, with some of these phases showing unconventional superconductivity with very large critical fields. At the core of this behavior are interactions between electron charge, electron spin and the lattice (the crystal structure). Critically important are the synthesis and growth of high quality samples for a detailed understanding of structure-property relationships. Structural characterization using diffraction techniques will be combined with investigations of physical properties, including magnetic susceptibility, electronic transport properties and optical properties. Furthermore, tuning of the physical properties by a combination of chemical substitutions and stoichiometry variations are explored. Crystal growth of such phases is well matched to the areas delineated in the National Academy of Sciences report "Frontiers in Crystalline Matter: From Discovery to Technology," which focuses on the opportunities for discovery and growth of crystalline matter in the US. This research is a highly interdisciplinary activity that requires a variety of skills. Training of students in the art and science of crystal growth and characterization of materials at undergraduate, graduate and postgraduate levels trains the next generation of scientists and engineers active in this field and builds the highly skilled workforce needed to address tomorrow's challenges.