1. Quasi One-Dimensional Vortex Flow Driven Through Mesoscopic Channels
Nobuhito Kokubo
Institute of Materials Science, University of Tsukuba
R. Besseling,
T. Sorop,
P. H. Kes
Kamerlingh Onnes Laboratory, Leiden University

2. Vortex flow J Fp = Jc B E hv = F J Jｃ E Driving force for vortices
Electric field due to vortex motion E
Pinning force for vortices
Fp = Jc B H
Baarle et al APL 2003 Jｃ J E
Driving force
velocity
Dissipations
in normal core(~px2)
hv = F

3. 1D Bardeen Stephen(BS) Formula
Vortex density B:
BS Formula for flux flow resistivity b b a l
Flow
BS Formula for 1D chain

4. 1D Vortex Flow in Twin Boundaries
A. Gurevich PRL, PRB 2002 b a
Abrikosov Josephson vortex

5. IV Curves in Twin Boundaries

6. Outline of This Talk
Vortex flow channel device
A short summary of previous results
New results
A kink anomaly in IV characteristics
ML experiments
Summary of this talk

7. Mesoscopic Vortex Flow Channels
0.2 – 1mm
Strong pinning NbN layer J H
Weak pinning a-NbGe layer J
w < l
SEM picture (w=650nm)

8. Matching Effects Matching condition Mismatch condition
The shear modulus
of vortex lattice c66
w=230 nm
0.4
0.8
1.2
1.0
2.0 ~c 66
(B) F p
(10 6
N/m 3 )
m0H (T)
experimental
data w
Mismatch condition
Matching condition b a f J

9. Mode Locking Experiments : Model
Coherent flow,
average velocity ‘v’
in pinning potential
fint = v/a
Lattice Mode :
Flow direction v a
Simplified picture
a: particle spacing // v
I= Idc + Irf sin(2pft )
ML occurs :
fint = p f
(vML = p a f)
Force
vML
Velocity

10. Mode Locking Experiments: Result
f=6MHz
Irf=0
Large Irf
p=1
p=2
p=3
w=230nm
weff b a
T<<Tc(NbGe)

11. Field Evolution of n and Fc
Vortex density
Oscillation in Fc is closely related with
the flow configurations in channels
PRL 88, (2002)

12. Field History in Channels
NbN
Field down (FD) mode
H is ramped down after applying a large field (>Hc2 of NbGe)
Field up (FU) mode
H is ramped up after ZFC
Field Focusing in channels
A decoration image in channels in a field of 50mT taken by N. Saha,
NbN
Quasi 1D flow properties
Conventional 2D FF behavior

13. Field History of Ic & IV Curves

14. H < H* 1D like vortex flow
Flow Resistance
Low I
High I
a = 0.5
H < H* 1D like vortex flow

15. Dynamic Change in Flow Structure
f (MHz) (= v/a)
f = fint = v/a at p=1
n = 3
n = 5 DC
A kink anomaly mark a dynamic change in flow configuration

16. Quasi 1D flow PropertiesH*
constant n
H < H* H*
n = 5
High RFB
n = 4
Quasi 1D flow properties
H > H*
Conventional (2D) Flux Flow
Low RFB
Lower R.F. branch : n
Higher R.F. branch: n+2
H* : 1D - 2D flow transition

17. Field profile in a channelFD
Mobile FU
Mobile

18. Summary
Mesoscopic channel system provides very rich physical properties
Field history changes the vortex dynamics in channels
Quasi-1D motion (square root dependence on field with constant flow configurations)
Dynamic change in flow configurations
Transition from quasi1D to 2D flow properties