Superconductivity in MgB2

Superconductivity in MgB2

Superconductivity Superconductivity in in MgB2 MgB2 Khalil Ziq Physics Department KFUPM April 12 2003 New Superconductor Developments .Fullerenes: Tc engineered to 117KIron 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

Ferromagnetism: EuB6 with S=7/2 4f-electron local moment and TC=16 K Ca1-xLaxB6 with 0.1 B/La and TC=600-1000 K CaB2C2 with 0.0001 B /f.u. and TC=770 K Superconductivit y: 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, MgB2

MgB2 Production Mg : B = 1:2 molar ratio Ground mixture for 15 minutes Pressed into 1g pellets Heat @800-950 C for . 2hours Structure The boron atoms form graphite-like sheets separated by hexagonal layers of Mg atoms. Equilibrium Magnetization Eqlm. Magnetization 0 Meq[G]

-25 4K 20K 30K -50 -75 -100 0 10000 20000 H[Oe]

30000 40000 London model 0 M=-Moln(Hc2/ H) Mo~^2 M[G] -5 -10

Evaluate Hc2, Hc and Mo -15 1000 10000 H[Oe] 40 20 0 0 10 20

30 40 T[K] 40000 30000 Hc2 [Oe] M0[G] 60 20000 10000

0 0 10 20 T [K] 30 40 Upper Critical Field Hc2 Along the c-Axis 6 5 4 Helfand-Werthamer

Ziq Welp et al. (T) c2 H 3 2 Tc 1 Sologubenko et al.

0 0 Angst et al. 10 20 T(K) 30 40 Perucchi et al., Phys. Rev. Lett . 89, 097001 (2002) Scaling of Meq

0.000 Meq/Hc -0.005 -0.010 -0.015 -0.020 -0.025 1 H/Hc 10

Hysteresis loops M/Hc 0.025 a 0.000 -0.025 H=2Hc H=4Hc 100 Jn=J/Hc (A/cm2/Oe) 4K 15K 25K 30K

35K 0.050 b 75 50 25 -0.050 0 2 4

6 h (H/Hc) 8 10 0 0 10 20 T(K) 30 40

Pinning force=H*Jc 6e+9 2 Pf (A O e/cm ) 4K 15K 25K 30K 4e+9 2e+9 0e+0 0

20000 H (Oe) 40000 Max. Pinning Force Fp(max) (Oe A/cm2) 1e+10 Hc Hirr Hc2 1e+9 1e+8 1e+7

1e+2 1e+3 1e+4 H(Oe) 1e+5 Conclusion Thermodynamic results supports clean limit SC, unlike optical results which support a dirty-limit scenario The superconducting gap with 2/kBTc~1.2 is substantially below the estimate of the weakcoupling BCS theory. The optical conductivity rises in an s-wave like manner.

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