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