Superconductivity in MgB2 Khalil Ziq Physics Department KFUPM April

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

The Borides World MgB2 Jan Jun Akimitsu APS March 2001 Ferromagnetism: EuB 6 with S=7/2 4f-electron local moment and T C =16 K Ca 1-x La x B 6 with 0.1  B /La and T C = K CaB 2 C 2 with  B /f.u. and T C =770 K Superconductivity: LNi 2 B 2 C with L=Lu, Tm, Er, Ho, Dy, Y) and T c =6-17 K MgB 2 with T c =39 K Boron: From the Arabic Buraq. Magnesium: District of Magnesia Greece,

MgB2

MgB 2 Production Mg : B = 1:2 molar ratio Ground mixture for 15 minutes Pressed into 1g pellets C for 2hours.

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

Equilibrium Magnetization

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

Perucchi et al., Phys. Rev. Lett. 89, (2002) Upper Critical Field H c2 Along the c-Axis Sologubenko et al. Helfand-Werthamer Welp et al. Angst et al. Ziq

Scaling of M eq

Hysteresis loops

Pinning force=H*Jc

Max. Pinning Force

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