Meso-Scale Correlated Electron Tunneling: Quantum Decay of the "False Vacuum" in the Laboratory
Date: Tuesday February 22, 2011
Time: 4:00 pm – 12:00 am
Location: Science & Research Building 1 – Building 550 — Room 634
This talk will outline new developments on time-correlated tunneling of electrons condensed into soliton domain walls in charge and spin density waves. The model treats the density wave as a quantum fluid in which condensed electrons coherently flow through a pinning barrier as soliton pairs nucleate via quantum decay of the "false vacuum." Experiments showing evidence for collective quantum tunneling up to 215 K, and the dual process of quantum nucleation of superconducting Josephson vortices, will be discussed. Finally, the talk will discuss broader implications, including bubble nucleation of universes and a proposed "theta = pi" instability for spontaneous CP violation formally similar to the "theta = pi" threshold field for soliton pair nucleation in density waves. Dr.
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IBAD-Textured Coated Conductors
by: Dr. Vladimir Matias
Date: Wednesday May 28, 2008
Time: 11:00 am – 12:00 pm
Location: Houston Science Center – Building 593 — Room 102
Second generation high temperature superconducting (HTS) wire, also known as coated conductor, holds great promise, thanks to its relatively low cost and high superconducting critical currents, to enable a number of superconducting power applications. In this talk we review some of the progress on ion-beam assisted deposition (IBAD) textured coated conductors. At Los Alamos National Laboratory we have developed processes for continuous texturing of MgO on metal tapes, buffer layer depositions, and HTS deposition by laser ablation and reactive coevaporation. IBAD-MgO texturing is the enabling process for these coated conductors. It is an extremely fast process but requires smooth surfaces over long lengths, which is achieved in our laboratory by electropolishing or sol-gel planarization of metal alloy tapes. The research to date has demonstrated that IBAD-MgO texture can develop in less than one second. Under optimized processing conditions the in-plane mosaic spread FWHM for the MgO layer is less than 5° and less than 2° out-of-plane. In the YBCO layer the texture improves further to less than 2° in-plane and 1° out-of-plane. At this level of grain alignment critical currents in HTS are no longer limited by the grain boundaries. Critical currents for YBCO layers deposited on the IBAD-MgO templates have been steadily increasing over the last 10 years, and have been demonstrated to exceed 600 A/cm-width. An important remaining issue for coated conductors is the decrease of Jc with thickness of the HTS layer. We discuss methods of addressing this issue as well as other key outstanding challenges.
This work is funded by the Department of Energy Office of Electricity Delivery & Energy Reliability.
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