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Experiments with semifluxon generator. Edward Goldobin University of Tübingen, Germany M. Paramonov, M. Fominsky, V. Koshelets IRE RAS, Moscow. [Logo of МОН 1.5 here]. Where is Tübingen?. Tübingen : small university town on r. Neckar population ~80000

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experiments with semifluxon generator

Experiments withsemifluxon generator

Edward Goldobin

University of Tübingen, Germany

M. Paramonov, M. Fominsky, V. Koshelets

IRE RAS, Moscow

[Logo of МОН 1.5 here]

where is t bingen
Where is Tübingen?
  • Tübingen:
  • small university town on r. Neckar
  • population ~80000
  • 30 km south from Stuttgart-- a capital of Baden-Württemberg
  • University:
  • students ~28000
  • university is 530 years old !!!
  • two faculties of theology ;-)
  • strong medicine
  • phys., chem., math are small
  • Our Group (~30 people):
  • 2 Profs: R. Kleiner, D. Koelle
  • 1 Assistant Prof.
  • 4 Post Docs
  • ~12 PhD students
  • ~10 Diploma students

Tübingen

josephson junction
Josephson junction

S

I

S

Conventional JJ. (0-junction)

I

+other terms

I

Unconventional JJ (p-junction)

S

I

S

jc=1–5000 A/cm2, (Nb-AlOx-Nb)

ybco nb ramp zigzags
YBCO-Nb ramp zigzags

LTSEM image of supercurrent

E. Goldobin, R. Straub, D. Dönitz,

D. Koelle, R. Kleiner,

H. Hilgenkamp (2003).

 H.-J. Smilde at al. PRL 88, 57004 (2002)

sfs sifs junctions
SFS/SIFS junctions

 V. Ryazanov et al. PRL 86, 2427 (2001)

 T. Kontos et al. PRL 89, 137007 (2002)

sine gordon equation for 0 p ljj
sine-Gordon equation for 0-p LJJ

— dimensionless damping

— dimensionless field

— the first critical field

Phase discontinuity points!

 Goldobin et al., PRB 66, 100508 (2002)

semifluxon vortex carrying f 0 2
Semifluxon=vortex carrying F0/2

Pinned, two degenerate states  and 

 Xu et al., PRB 51, 11958 (1995)

 Goldobin et al., PRB 66, 100508 (2002)

semifluxons observation
Semifluxons observation

SQUID microscopy on YBCO-Nb ramp zigzag LJJs

 H. Hilgenkamp et al. Nature 422, 50 (2003).

artificial 0 k junctions
Artificial 0-k junctions

A. Ustinov, Appl. Phys. Lett. 80, 3153 (2000).

Goldobin et al., Phys. Rev. Lett. 92, 057005 (2002)

nb ljj with two injectors
Nb LJJ with two injectors

lJ  30 mm (jc 100 A/cm2)

calibration of injectors
Calibration of injectors

Numerical

Experimental

Goldobin et al., PRL 92, 057005 (2004)

switching on the current
Switching on the current...
  • at zero bias we have a static pinned semifluxon.
  • bias current pulls semifluxons, just like fluxons.
  • but semifluxons are pinned --> deformation
  • at bias=2/ Ic0.64 Ic switching to the R-state

 Goldobin et al., PRB 67, 224515 (2003).

overcritical bias oscillator
Overcritical bias:oscillator

magnetic field

  • Frequency depends on:
    • bias current, damping, length
    • two outputs shifted by 180°
    • more stable than flux-flow due to semifluxon pinning

voltage

 N. Lazarides, PRB69, 212501 (2004).

semifluxon half integer zfs
Semifluxon -- half-integer ZFS
  • Finite length --> image technique:
    • 1 real semifluxon + 2 anti-semifluxons (images)
  • Bias current  Force SF hopping.

Goldobin et al., Phys. Rev. B 67, 224515 (2003).

half integer zfs full ivc
Half integer ZFS (full IVC)

Goldobin et al., PRL 92, 057005 (2004)

half integer zfs
Half integer ZFS

Goldobin et al., PRL 92, 057005 (2004)

layout
Layout

L = 16..32 mm

dx=dw=1, 1.5, 2 mm

emission lines
Emission lines

Different bias points along the semifluxon step

Autonomous linewidth ~1.2 … 10 MHz

and now with pll
And now with PLL ;-)

with PLL the spectral ratio is up to 97%

summary problems
Summary & Problems

Summary

  • many samples work (both generator and detector)
  • we observe expected operation:
  • a semifluxon step, SIS pumping
  • we have measured autonomous linewidth
  • ..and linewidth with PLL

Outlook (problems & todos):

  • maximum Ic in Ic(H) and Ic(Iinj) are not equal
  • in high freq. setup strange shunt resistance of ~3 Ohm
  • in high freq. setup strange dep. of voltale on Iinj.
  • Repeat again with remaining 2 samples and try to make new ones.
  • Compare linewidth with inj with the one with CL.
  • Compare with ZFS
  • not all LO freq were good
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