Superconductivity%20in%20MgB2

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Superconductivity in MgB2

• Khalil Ziq
• Physics Department
• KFUPM
• April 12 2003

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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).

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The Borides WorldMgB2 Jan 10 2001 Jun
AkimitsuAPS March 2001
Ferromagnetism EuB6 with S7/2 4f-electron local
moment and TC16 K Ca1-xLaxB6 with 0.1 mB/La and
TC600-1000 K CaB2C2 with 0.0001 mB /f.u. and
TC770 K
Superconductivity LNi2B2C with LLu, Tm, Er, Ho,
Dy, Y) and Tc6-17 K MgB2 with Tc39 K
Boron From the Arabic Buraq. Magnesium District
of Magnesia Greece,
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MgB2
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MgB2 Production

• Mg B 12 molar ratio
• Ground mixture for 15 minutes
• Pressed into 1g pellets
• Heat _at_800-950 C for 2hours.

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Structure
The boron atoms form graphite-like sheets
separated by hexagonal layers of Mg atoms.
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Equilibrium Magnetization
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M-Moln(Hc2/H)Mo?2
Evaluate Hc2, Hc and Mo
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Upper Critical Field Hc2 Along the c-Axis
Ziq
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Scaling of Meq
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Hysteresis loops
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Pinning forceHJc
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Max. Pinning Force
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Conclusion

• Thermodynamic results supports clean limit SC,
  unlike optical results which support a
  dirty-limit scenario
• The superconducting gap with 2D/kBTc1.2 is
  substantially below the estimate of the
  weak-coupling BCS theory.
• The optical conductivity rises in an s-wave like
  manner.