Semifluxon Generator Experiments at University of Tübingen

1. Experiments withsemifluxon generator Edward Goldobin University of Tübingen, Germany M. Paramonov, M. Fominsky, V. Koshelets IRE RAS, Moscow [Logo of МОН 1.5 here]

2. 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

3. 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)

4. Long Josephson 0- junction x 1D model 0 p

5. 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)

6. SFS/SIFS junctions  V. Ryazanov et al. PRL 86, 2427 (2001)  T. Kontos et al. PRL 89, 137007 (2002)

7. 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)

8. Semifluxon=vortex carrying F0/2 Pinned, two degenerate states  and   Xu et al., PRB 51, 11958 (1995)  Goldobin et al., PRB 66, 100508 (2002)

9. Mechanical analog:pendula chain f(x) m(x)

10. Semifluxons observation SQUID microscopy on YBCO-Nb ramp zigzag LJJs  H. Hilgenkamp et al. Nature 422, 50 (2003).

11. Artificial 0-k junctions  A. Ustinov, Appl. Phys. Lett. 80, 3153 (2000). Goldobin et al., Phys. Rev. Lett. 92, 057005 (2002)

12. Nb LJJ with two injectors lJ  30 mm (jc 100 A/cm2)

13. Calibration of injectors Numerical Experimental Goldobin et al., PRL 92, 057005 (2004)

14. 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).

15. 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).

16. 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).

17. Half integer ZFS (full IVC) Goldobin et al., PRL 92, 057005 (2004)

18. Half integer ZFS Goldobin et al., PRL 92, 057005 (2004)

19. Experiments last week in IRE

20. Layout L = 16..32 mm dx=dw=1, 1.5, 2 mm

21. Calibration: Ic(ICL) & Ic(Iinj)

22. I-V characteristic of generator

23. SIS detector

24. Emission lines Different bias points along the semifluxon step Autonomous linewidth ~1.2 … 10 MHz

25. And now with PLL ;-) with PLL the spectral ratio is up to 97%

26. 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