Session L1: Basic Research Needs for Superconductivity

Superconductivity: Challenges and Opportunities

As part of its effort to define transformational opportunities for fundamental research in energy security, the Department of Energy's Office of Basic Energy Sciences held a workshop on Basic Research Needs for Superconductivity. The workshop identified a number of materials grand challenges and priority research directions for transforming the power grid to meet the needs of the 21st century. The prospect of moving from materials by serendipity to materials by design and of advancing the frontiers of epitaxial science to yield higher performing nano-structured architectures are two of the these challenges that could impact superconductivity research specifically and materials research more broadly. In this talk we highlight recent technical successes that motivate and illustrate these opportunities. We also discuss the science that might be necessary to accomplish these goals in the hopes of nucleating further community input and engagement. In collaboration with Wai Kwok, Argonne National Laboratory.   

Approaches to New Superconducting Materials

Over the last twenty years a large set of new superconductors with extraordinary properties have been discovered and studied. They are all by any measure complex materials, involving several elements arranged in complex crystal structures. Even the normal states of these materials exhibit highly correlated behavior, and the superconducting states are equally unusual, with complex order parameter symmetries, exotic vortex behavior and strong dependence on carrier doping. In the future, new complex materials that are chemically stable compounds will certainly continue to be found, at least some of which may result from rational searches. There is also an opportunity to create new materials in which the molecular, electronic, spin and phonon structure that sets the stage for the emergence of a superconducting state is defined artificially. Such ``meta-materials'' allow for the factors that are important for an emergent state to be included in new ways, and they also provide a test bed for predictive theory. Oxides are particularly well suited for this kind of work, since heterojunctions between different phases can be formed in many cases with little disorder. In other correlated systems, some new and useful properties not found in naturally occurring compounds have been engineered this way by researchers in several labs. Many heterojunction issues governing the resulting electronic and magnetic structure remain to be systematically studied, including state line-up, charge transfer, interface composition and bond energies to name a few.   

Structure and Dynamics of Vortex Matter

The DOE Basic Energy Sciences Workshop on Basic Research Needs for Superconductivity identified grand challenges and research priorities for \textit{discovery} and \textit{use inspired} basic research to transform the US power grid to meet the needs of the 21$^{st}$ century. Vortex matter research is central to this endeavor and helps support both fundamental and applied research. The science of vortex matter embodies the fundamental mysteries of vortex-vortex interactions in an inhomogeneous and anisotropic matrix. Understanding the complex phase diagrams and the dynamic responses that result from these competing effects is an outstanding challenge. Simultaneously, the prospect of controlling these interactions opens new horizons for basic research such as the development of a microscopic theory for vortex dynamics, exploration of vortex nucleation at magnetic and superconducting interfaces and designs for pinning a vortex liquid at high temperatures. This presentation will highlight ways in which nanotechnology based methodologies, dynamic vortex creep phenomena and powerful computer simulations play a role in enhancing our understanding of next-generation and new classes of superconductors.   

Understanding of Mechanisms for Design of Advanced Superconductors

A recent DOE panel considered the future of research in superconducting materials and made a number of recommendations for priority research directions ({\it http://www.er.doe.gov/bes/reports/files/SC\_rpt.pdf}), two of which will be discussed. These items, under the rubric of {\it Enabling Superconductivity}, emphasize that {\it Finding the Mechanisms} is essential for furthering the field, and that once understood, the prospect of {\it Superconductors by Design} becomes a viable line of research. Establishing the mechanism in the high temperature superconducting cuprates continues to attract substantial efforts, with no consensus near. In several superconductors, including some discovered in the past decade or so, having T$_c$ around or above 20 K [(Ba,K)BiO$_3$; Li$_x$HfNCl; PuCoGa$_5$] the mechanism is in question. On the more positive side, there are several cases established in the past six years, beginning with MgB$_2$ and extending to elemental metals under pressure (Li, Y, Ca), where the familiar electron-phonon mechanism has provided unexpectedly high T$_c$ and thereby stimulated enthusiasm and optimism into this area of superconductivity research. The clear understanding of this mechanism (at least in many respects) provides a path for improvements in superconducting materials.   

Transforming the Grid with Superconductivity

The electric power grid in the United States faces critical challenges: overloading caused by years of limited investment and steady load growth, bottlenecks in power corridors into urban centers, voltage instability leading to brownouts and blackouts, growing fault currents in large urban and suburban areas, as well as the need for increased efficiency. Power equipment based on high temperature superconductors (HTS) offers solutions to these challenges: high capacity, non-interfering HTS cables addressing power bottlenecks, HTS fault current limiters controlling fault currents, HTS synchronous condensers and novel controllability features of HTS cables which address stability issues, HTS transformers and generators with increased efficiency. A variety of commercial-level demonstrations make the impact of HTS power equipment imminent.