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