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Condensed Matter Seminar: Vortex Pinning and Critical Currents in Iron Based Superconductors

SpeakerDr. Wai-Kwong Kwok - Senior Scientist & Group Leader - Superconductivity and Magnetism Group - Materials Science Division - Argonne National Laboratory (IL)    
Date Nov 16, 2012
Time 1:00 pm  
Location 190 Engineering Sciences Bldg - corner Goodwin & Springfield 
Sponsor Physics
Contact Peggy Pennell
Phone 217/244-7636
Event type Seminar/Symposium
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The search for an isotropic high transition temperature (Tc) superconductor with high current carrying capacity (critical current, Jc) is one of the grand challenges in basic superconductivity research.  Such a material would improve the applicability of high temperature superconductors to electricity transmission and enable their use in rotating machinery, such as electric motors and wind turbines, for which anisotropy is an impediment.  A few years ago, multi-band, iron-pnictide superconductors with relatively high Tc and low anisotropy were discovered, potentially moving us closer to that goal.  I will present some of our recent work aimed at enhancing the critical current and further lowering the anisotropy in these materials via doping and particle irradiation.  In particular, I will describe the doping dependence of vortex pinning behavior in phosphor-doped isovalent BaFe2(As1−xPx)2 and the pronounced enhancement of the critical current and reduction of the superconducting anisotropy that we have achieved with heavy-ion irradiation in optimally-doped BaKFe2As2 and SmFeAs(O1-xFx) crystals. I will also show how composite (correlated plus point) defects induced by a combination of heavy-ion and proton irradiation further enhanced the critical current in these materials.  Comparisons with the critical currents of state-of-the-art 2nd generation YBCO coated conductors show that iron pnictide superconductors can rival the vortex pinning of cuprates at high magnetic fields.  Understanding these materials may eventually allow us to tune the multi-band structure to produce isotropic superconductors with even higher transition temperatures and critical currents.

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