Bulletin of the American Physical Society
78th Annual Meeting of the Southeastern Section of the APS
Volume 56, Number 9
Wednesday–Saturday, October 19–22, 2011; Roanoke, Virginia
Session KA: Superconductivity: 100th Anniversary |
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Chair: Norman Mannella, University of Tennessee Room: Crystal Ballroom A |
Friday, October 21, 2011 3:45PM - 4:15PM |
KA.00001: A New Piece in the High $T_c$ Superconductivity Puzzle: Fe based Superconductors Invited Speaker: An overview of the historic and current developments in superconductivity will be be presented. The phenomenon of superconductivity was discovered almost 100 hundred years ago and it is still one of the hottest research topics providing fascinating puzzles and challenges to both theoreticians and experimentalists. There was a lag of almost 50 years between the experimental discovery of (low $T_c$) superconductivity and the development of the BCS theory which explained the phenomenon in terms of pairs of electrons held together by the interaction with the phonons in the material. The quest to discover superconducting materials with higher $T_c$'s continued quietly for many years until huge progress occurred in the 1980' when $T_c$'s higher than 77K were observed in copper-oxide based materials. The study of these new materials generated tremendous advances in both experimental and theoretical methods and much is now known about their properties; but the mechanism, i.e., the ``glue,'' that binds the electrons together is still unknown; it appears that phonons are unable to do the job and there is controversy on whether the magnetism present in these materials helps or hurts. Very recently, in 2008, high $T_c$ was discovered in a new family of iron based materials. While they are similar to the cuprates in some ways, i.e., magnetism is present, there are many differences as well. This discovery provides a new chance to unveil the high-$T_c$ mystery and the condensed matter community is intensely working on the subject. [Preview Abstract] |
Friday, October 21, 2011 4:15PM - 4:45PM |
KA.00002: High Temperature Superconductors: From Basic Research to High-Current Wires Invited Speaker: In this talk, I will provide a perspective on the fundamental properties of the cuprate high-temperature superconductors (HTS), and how early and ongoing fundamental research has identified the strengths and weaknesses, and has ultimately led to the development of superconducting wires for power applications--the so-called ``coated conductors.'' Early work on the properties of various classes of cuprate HTS materials revealed their emergent behavior as type-II superconductors, even though it was apparent that the underlying pairing mechanism is likely quite different than for conventional, electron-phonon coupled materials. From the perspective of this talk, important findings documenting the level of electronic anisotropy, basic length scales, etc., and the effects of thermal energies on vortex matter are described, especially as they relate to the ability to carry loss-free currents. It became apparent that good supercurrent conduction was achieved only along well-aligned basal planes of the structure, and enhancement of those currents could be obtained by introduction of controlled nanostructures for flux pinning. From this work, the (RE)Ba$_{2}$Cu$_{3}$O$_{7-\delta }$ emerged as the best material class for potential high-current wires, mainly because it was the least anisotropic from among those with transition temperature exceeding the boiling point of liquid nitrogen. Ultimately, much effort has been devoted to the control and optimization of nanostructural modifications to the materials, at a size range and spacing that should be tailored to match the magnetic vortex array. The description, success, and consequences of these efforts will be presented. [Preview Abstract] |
Friday, October 21, 2011 4:45PM - 5:15PM |
KA.00003: New challenges and opportunities for high-$T_c$ superconducting materials Invited Speaker: Since its discovery 100 years ago, superconductivity has captured the imagination of many as a fascinating physical phenomenon which would enable the drastic reduction of energy waste in the electric power grid, high field magnets and large accelerators. Understanding the physics of superconductivity has been advancing along with the discovery of many superconducting materials and tuning their properties. In this talk I will give a brief overview of how the physics of unconventional superconductivity turned out to be intertwined with materials properties, with the emphasis on high-$T_c$ cuprates and the recently discovered Fe-based superconductors. One of the lessons of the last 20 years is that high critical temperatures and upper critical magnetic fields of unconventional superconductors are no longer the main parameters of merit for power applications, which can also be important for the ongoing quest for higher-$T_c$ materials. [Preview Abstract] |
Friday, October 21, 2011 5:15PM - 5:45PM |
KA.00004: Evolution of spin excitations in high-temperature iron-based superconductors Invited Speaker: In this Talk, I describe the most recent progress in the field of iron-based superconductors. Using neutron scattering as a probe, we study the spin wave excitations in BaFe2As2 and RbFe1.6Se2, and its electron/hole doping evolution of the spin excitations. We find that the effective next nearest neighbor (NNN) exchange interactions for different families of materials are rather similar, thus demonstrating that the common features for superconductivity is associated with the NNN exchange interactions in these materials. These results suggest that spin excitations are the most promising candidate for electron pairing and superconductivity in iron-based superconductors, regardless of their original antiferromagnetic ordering status and electronic structure. [Preview Abstract] |
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