Superconductivity in MgB2 Khalil Ziq Physics Department KFUPM April 12 2003.
17
Superconductivity in Superconductivity in MgB2 MgB2 Khalil Ziq Khalil Ziq Physics Department Physics Department KFUPM KFUPM April 12 2003 April 12 2003
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Transcript of Superconductivity in MgB2 Khalil Ziq Physics Department KFUPM April 12 2003.
Superconductivity in Superconductivity in MgB2MgB2
Superconductivity in Superconductivity in MgB2MgB2
Khalil Ziq Khalil Ziq Physics DepartmentPhysics Department
KFUPMKFUPMApril 12 2003April 12 2003
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 WorldMgB2 Jan 10 2001
Jun AkimitsuAPS March 2001
Ferromagnetism:EuB6 with S=7/2 4f-electron local moment and TC=16 KCa1-xLaxB6 with 0.1 B/La and TC=600-1000 KCaB2C2 with 0.0001 B /f.u. and TC=770 K
Superconductivity:LNi2B2C with L=Lu, Tm, Er, Ho, Dy, Y) and Tc=6-17 KMgB2 with Tc=39 KBoron: From the Arabic Buraq.
Magnesium: District of Magnesia Greece,
MgB2
MgB2 Production
•Mg : B = 1:2 molar ratioGround mixture for 15 minutesPressed 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
H[Oe]
0 10000 20000 30000 40000
Meq
[G]
-100
-75
-50
-25
0
4K20K30K
M=-Moln(Hc2/H)Mo~λ^2
London model
H[Oe]
1000 10000
M[G
]
-15
-10
-5
0
Evaluate Hc2, Hc and Mo
T[K]
0 10 20 30 40
M0[
G]
0
20
40
60
T [K]
0 10 20 30 40
Hc2
[O
e]
0
10000
20000
30000
40000
Perucchi et al., Phys. Rev. Lett. 89, 097001 (2002)
Upper Critical Field Hc2 Along the c-Axis
0 10 20 30 400
1
2
3
4
5
6
T(K)
H c2 (T)
Tc
Sologubenko et al.
Helfand-Werthamer
Welp et al.
Angst et al.
Ziq
Scaling of Meq
H/Hc1 10
Meq
/Hc
-0.025
-0.020
-0.015
-0.010
-0.005
0.000
Hysteresis loops
h (H/Hc)
0 2 4 6 8 10
M/H
c
-0.050
-0.025
0.000
0.025
0.0504K15K25K30K35K
a
T(K)
0 10 20 30 40
Jn=
J/H
c (A
/cm
2 /Oe
)
0
25
50
75
100
H=2HcH=4Hc
b
Pinning force=H*Jc
H (Oe)0 20000 40000
Pf
(A O
e/c
m2 )
0e+0
2e+9
4e+9
6e+94K15K25K30K
Max. Pinning Force
H(Oe)
1e+2 1e+3 1e+4 1e+5
Fp(
max
) (O
e A
/cm
2 )
1e+7
1e+8
1e+9
1e+10
Hc HirrHc2
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 weak-coupling BCS theory.
The optical conductivity rises in an s-wave like manner.
Conclusion
