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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

Superconductivity in MgB2

Khalil Ziq

Physics Department

KFUPM

April 12 2003

new superconductor developments
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).

the borides world mgb2 jan 10 2001 jun akimitsu aps march 2001
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,

mgb 2 production
MgB2 Production
  • Mg : B = 1:2 molar ratio

Ground mixture for 15 minutes

Pressed into 1g pellets

  • Heat @800-950 C for 2hours.
structure
Structure

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

m mo ln hc2 h mo 2
M=-Moln(Hc2/H)Mo~λ^2

Evaluate Hc2, Hc and Mo

upper critical field h c2 along the c axis

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)

slide17

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.