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Superconductivity in MgB2

Superconductivity in MgB2. Khalil Ziq Physics Department KFUPM April 12 2003. New Superconductor Developments. -Fullerenes: T c engineered to 117K. -Iron and Sulfur become SC under pressure. -Plastic SC: polythiophene. -DNA can be made superconducting.

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Superconductivity in MgB2

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  1. Superconductivity in MgB2 Khalil Ziq Physics Department KFUPM April 12 2003

  2. New Superconductor Developments -Fullerenes: Tc engineered to 117K. -Iron and Sulfur become SC under pressure. -Plastic SC: polythiophene. -DNA can be made superconducting. -MgB2 changes our thinking (again).

  3. The Borides WorldMgB2 Jan 10 2001Jun AkimitsuAPS March 2001 Ferromagnetism: EuB6 with S=7/2 4f-electron local moment and TC=16 K Ca1-xLaxB6 with 0.1 mB/La and TC=600-1000 K CaB2C2 with 0.0001 mB /f.u. and TC=770 K Superconductivity: LNi2B2C with L=Lu, Tm, Er, Ho, Dy, Y) and Tc=6-17 K MgB2 with Tc=39 K Boron: From the Arabic Buraq. Magnesium: District of Magnesia Greece,

  4. MgB2

  5. MgB2 Production • Mg : B = 1:2 molar ratio Ground mixture for 15 minutes Pressed into 1g pellets • Heat @800-950 C for 2hours.

  6. Structure The boron atoms form graphite-like sheets separated by hexagonal layers of Mg atoms.

  7. Equilibrium Magnetization

  8. M=-Moln(Hc2/H)Mo~λ^2 Evaluate Hc2, Hc and Mo

  9. Helfand-Werthamer Welp et al. Sologubenko et al. Angst et al. Upper Critical Field Hc2 Along the c-Axis Ziq Perucchi et al., Phys. Rev. Lett. 89, 097001 (2002)

  10. Scaling of Meq

  11. Hysteresis loops

  12. Pinning force=H*Jc

  13. Max. Pinning Force

  14. Conclusion • Thermodynamic results supports clean limit SC, unlike optical results which support a dirty-limit scenario • The superconducting gap with 2D/kBTc~1.2 is substantially below the estimate of the weak-coupling BCS theory. • The optical conductivity rises in an s-wave like manner.

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