Pinning Effect on Niobium Superconducting Thin Films with Artificial Pinning Centers.

Lance Horng, J. C. Wu, B. H. Lin, P. C. Kang, J. C. Wang, and C. W. HsiaoNational Changhua University of Education, Changhua

T. C. Wu and T. J. YangNational Chiao Tung University, Hsinchu

OUTLINE

1.Motivation2.Experimental methods:

Fabrication – electron beam lithography

Measurement – four-probe measurement

3.Results and Analysis Artificial pinning arrays of pinning sites Square arrays Triangular arrays Honeycomb arrays

4.Conclusions

Magnetic property

Schematic drawing for flux flowing

c

Jf 0

cBE

J

EI

B

I

sisi

Electron Beam

si

Electron Beam

si

sisi

A B C

E-beam Writing Development

D ERIE etching Si3N4

Si

Nb films

Opening cross trenches in PMMA

Nb sputtering Cross section

Si3N4siSi3N4Si3N4si

Electron Beam

si

Electron Beam

si

Fabrication

Keithley-224

Keithley-182

樣品位

置

J. Appl. Phys. 91, 8510 (2001)

Jpn. J. Appl. Phys. 42, 2679 (2003)

Square arrays of pinning sites

Field dependence of the resistance and critical current for a Nb film with a square array of defects at T=8.75 K.

AFM image of the patterned films

-500 -400 -300 -200 -100 0 100 200 300 400 5001E-5

1E-4

1E-3

0.01

0.1

1

10 n=3 n=2 n=3n=2n=1 n=1

8.75 K Res (

Om

h)

Field (G)

30uA 100uA 300uA

mobile interstitial vortices

Molecular dynamics simulations of vortex states

Vortex configurationsat integer matchingfields in squarepinning array

C. Reichhardt et al., Phys. Rev. B 57, 7937 (1998)

Magnetoresistance curves taken at T = 8.73 K for different currents for this sample.

AFM image of the Nb films

Triangular arrays of pinning sites

I-V characteristics for a triangle lattice at T=8.73 K under various magnetic fields applied perpendicular to the film plane.

I

I

Case A Case B

SEM micrograph of the patterned sample.

Schematic of the current geometry relative to the rhombic unit cell.

Critical current as a function of the magnetic field for a Nb film with a triangular array of defects.

The vortices distribution (filled circles) and pinning sites (open circles) for (a) the incommensurate row and (b) the interstitial flowing channel.

2

22

811.4

4.02

33

2

233

2

m

a

np

2

22

217.7

4.043

21

43

21

m

a

np

2831.4

mB

no

v

a

a3

a

AFM image of the patterned sample. The depth of holes is around 70 nm

SEM micrograph of the patterned sample. The honeycomb array of corrugated holes with spacing of 400 nm and hole diameter of around 200nm embedded in the 100 nm thick superconducting Nb thin films

0 50 100 150 200 250 300 350 400 450 500 550 6001E-3

0.01

0.1

1

5.04.03.02.01.0n=

R (

Ohm

)

H (Oe)

8.11K 8.12K 8.13K 8.14K 8.16K

n = 0.5 n = 1.0 n = 1.5

n = 2.0 n = 2.5 n = 3.0 n = 3.5

Schematic of the Vortex states that are possible for n = B / ∆B = 0.5, 1.0, 1.5, 2.0, 2.5, 3.0, and 3.5.

Conclusion

Flux-line confinement by a array of sub-micrometer holes has been studied in a superconducting Nb film of corrugated pinning sites.

The matching effects observed in the MR and Ic(H) curves are related to the flux pinning caused by the array of defects.

The interplay between nanostructured superconductors and Abrikosov vortex lattice is a powerful tool to explore motion of particles in different scenarios.