Experiments with semifluxon generator

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Experiments withsemifluxon generator
Edward Goldobin University of Tübingen,
Germany M. Paramonov, M. Fominsky, V.
Koshelets IRE RAS, Moscow
Logo of ??? 1.5 here
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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
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Josephson junction
Conventional JJ. (0-junction)
I
other terms
I
Unconventional JJ (p-junction)
S I S
jc15000 A/cm2, (Nb-AlOx-Nb)
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Long Josephson 0-? junction
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YBCO-Nb ramp zigzags
E. Goldobin, R. Straub, D. Dönitz, D. Koelle, R.
Kleiner, H. Hilgenkamp (2003).
? H.-J. Smilde at al. PRL 88, 57004 (2002)
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SFS/SIFS junctions
? V. Ryazanov et al. PRL 86, 2427 (2001)
? T. Kontos et al. PRL 89, 137007 (2002)
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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)
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Semifluxonvortex carrying F0/2
Pinned, two degenerate states ? and ?
? Xu et al., PRB 51, 11958 (1995)
? Goldobin et al., PRB 66, 100508 (2002)
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Mechanical analogpendula chain
f(x)
m(x)
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Semifluxons observation
SQUID microscopy on YBCO-Nb ramp zigzag LJJs
? H. Hilgenkamp et al. Nature 422, 50 (2003).
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Artificial 0-k junctions
A. Ustinov, Appl. Phys. Lett. 80, 3153 (2000).
Goldobin et al., Phys. Rev. Lett. 92, 057005
(2002)
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Nb LJJ with two injectors
lJ ? 30 mm (jc ? 100 A/cm2)
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Calibration of injectors
Numerical
Experimental
Goldobin et al., PRL 92, 057005 (2004)
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Switching on the current...

• at zero bias we have a static pinned semifluxon.
• bias current pulls semifluxons, just like
  fluxons.
• but semifluxons are pinned --gt deformation
• at bias2/? Ic?0.64 Ic switching to the R-state

? Goldobin et al., PRB 67, 224515 (2003).
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Ic(H) of long 0-p JJ
? N. Lazarides, PRB 69, 212501 (2004).
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Overcritical biasoscillator
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, PRB 69, 212501 (2004).
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Semifluxon -- half-integer ZFS

• Finite length --gt image technique
• 1 real semifluxon 2 anti-semifluxons (images)
• Bias current ? Force ? SF hopping.

Goldobin et al., Phys. Rev. B 67, 224515 (2003).
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Half integer ZFS (full IVC)
Goldobin et al., PRL 92, 057005 (2004)
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Half integer ZFS
Goldobin et al., PRL 92, 057005 (2004)
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Experiments last week in IRE
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Layout
L 16..32 mm dxdw1, 1.5, 2 mm
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Calibration Ic(ICL) Ic(Iinj)
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I-V characteristic of generator
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SIS detector
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Emission lines
Different bias points along the semifluxon step
Autonomous linewidth 1.2 10 MHz
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And now with PLL -)
with PLL the spectral ratio is up to 97
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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