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Double re-entrant superconductivity in SF-Hybrids A. S. Sidorenko

Mesoscopic and strongly correlated systems Chernogolovka, 11-16.10. 2009. Double re-entrant superconductivity in SF-Hybrids A. S. Sidorenko Institute of Electronic Engineering ASM, Kishinev, Moldova In collaboration with: Kazan State University, Kazan, Russia - L. R. Tagirov

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Double re-entrant superconductivity in SF-Hybrids A. S. Sidorenko

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  1. Mesoscopic and strongly correlated systems Chernogolovka, 11-16.10. 2009 Double re-entrant superconductivity in SF-Hybrids A. S. Sidorenko Institute of Electronic Engineering ASM, Kishinev, Moldova In collaboration with: Kazan State University, Kazan, Russia - L. R. Tagirov Institute for Solid State Physics of RAS, Chernogolovka, Russia- V.V. Ryazanov, V.Oboznov Universität Augsburg, Germany - M. Schreck, G.Obermeier, C. Müller, S. Horn, R. Tidecks Karlsruhe Institute of Technology, Germany – H.Hahn, E.Nold Moscow State University, Russia – M.Yu. Kupriyanov

  2. ESF Exploratory Workshop Paestum (Salerno), Italy, 20-21 June 2008 O U T L I N E 1. Coexistence of S-F, FFLO state 2. Proximity effect in S/F layers, quasi-1D FFLO 3. Novel technology-->Re-entrant superconductivity 4. Conclusions

  3. 1) FFLO state P. Fulde, R. A. Ferrell Phys.Rev. 135 (1964) A550 A. I. Larkin, Yu. N. Ovchinnikov JETP 47 (1964) 1138 Non uniform SC state with: - nonzero pairing momentum, q0=kF ≠ 0 - oscillating pairing function, F~cos(kFx). Singlet pairs in a ferromagnet - non uniformFFLO pairing Exchange field splitsconduction band of ferromagnet

  4. FFLO state: Eex/0 Strict limitation: 0,71 0 < Eex < 0,76 0 Eex ~ 0.1-1 eV 0 ~ 0.001 eV

  5. 2) FFLO-like1D-state Proximity-effect: F S N De Gennes, Rev.Mod.Phys.36 (1964)225 x S F A. Buzdin, Z. Radović, PR B38 (1988) 2388 x In F-layer: nonzero pairing momentum , q0 ~ Eex≠ 0,FFLO-like state FF oscillates on magnetic coherence length, 2 =F = ħvF/Eex and relaxes on decay length, 1=lF

  6. Interference of Pairing Function In F-layer: Fabry-Perot interferometer analogy F Vacuum S dF

  7. Oscillations of superconducting Tc as a function of the ferromagnetic layer thickness in multilayers Z. Radovich et al, PRB 44, 759 (1991) π-phase 0-phase

  8. non monotonous TC(dF) for S/F : t=Tc/TcS A. Buzdin, Z. Radović, PR B38 (1988) 2388 ln t = (½) – Re( ½ + r/t ) A lot of attempts – controversial results: dF/F Nb/Gd Ch.Strunk, PRB 49 (1994) 4053 (MBE) – nooscil. J.Jiang, PRL 74 (1995) 314 (dc-magnetron) – oscil. Nb/Fe G.Verbank,PRB57 (1998) 6029 (MBE) – nooscil. I.Garifullin, PRB 55 (1997) 8945 (dc-magnetron) - oscil. Nb/CuMn C.Attanasio, PRB 57 (1998) 14411 (dc-magnetron) – oscil. Nb/CuNi V.Ryazanov et al., JETP Lett. 77 (2003) 43(dc-magnetron) – oscil.

  9. Experimentals • Our choice: • dc magnetron sputtering • atomic smooth substrate (flame polished glass ) • Nb/Ni couple (Nb-Ni solubility less than 4 at.%) - single-run deposition process

  10. magnetron sputtering Nb/Ni samples 5-8nm 20-70 nm

  11. XRD RBS Thickness measurement accuracy: dNi ± 0.03 nm Roughness: rms < 0.3 nm

  12. TC oscillation in Nb/Ni bilayer:quasi-1D FFLO state L. R. Tagirov, Phys. C 307 (1998) 145 A. Sidorenko, V. Zdravkov, A.Prepelitsa et al., Ann. Phys. 12 (2003) 37. dF/F (Curves 1-5: variable interface transparency, Tm= 5, 2.5, 1.25, 0.5, 0.25)

  13. 3). Re-entrant superconductivity Calculation for S/F sandwich – oscillations TC up to re-entrance: dF/F Tcs-The temperature of SC transition for single layer S,M - SC coherence lengths in SC and FM dS,M - thicknesses of SC and FM layers

  14. Re-entrant superconductivity: pilot experiments with Nb/Cu43Ni57 V.Ryazanov et al., Pisma JETP Lett. 77, 43 (2003); hint: CuNi layer thickness to observe the re-entrant Tc has to be 2 - 8 nm

  15. Our pilot experiments with Nb/Cu0.41Ni0.59 1)dS, / S ~ 1 dS, ~ 10nm 2)alloy Cu0.41 Ni0.59ξF = ħvF/Eex~ 8nm (allows larger thicknesses dF of about 5-10 nm ) The necessity of technology development for ultra-thin S and F layers preparation

  16. Sample preparation- Novel Technology :Sidorenko A.S., Zdravkov V.I., “Instalaţie pentru obţinere peliculelor conductoare”, Patent of RM №3135 from 31.08 2006. moving target • DC magnetron sputtering a) high deposition rate (4 nm/s) b) moving Nb target (precisely constant S-layer thickness) Nb-target with holder:

  17. 1. Superconducting properties of prepared Nb films IEEIT Critical temperatures for Nb films with thickness 5.5-14 nm

  18. Si CuNi Nb Si Nb Substrate (Si) Sample preparation - Novel Technology :Sidorenko A.S., Zdravkov V.I., “Instalaţie pentru obţinere peliculelor conductoare”, Patent of RM №4831 from 28 June 2006. • DC, RF- magnetron sputtering with high rate • Deposition in one run of the structure with constant «S» (Nb) and wedge-like «F» (CuNi on shifted substrate)layer • Deposition of long (80 mm) Nb films with constant thickness • Protection of the sample by covering Si-layer.

  19. Si-Substrat 2. TEM of Nb/CuNi structures Nb/CuNi 22#18 IEEIT Si-Substrate Si-Buffer Nb CuNi Si-Cap dCuNi= 14.1nm dNb = 6nm

  20. Si N Si Sub 2. Investigation of the morphology of prepared Nb films and S/F nanostructures (AFM, XRD, SEM, RBS, Auger) IEEIT SEM measurements of Nb film

  21. Workshop Karlsruhe, 13-17 July 2008 2. SEM measurements of Nb/CuNi structures IEEIT

  22. IEEIT 2. Auger measurements of Nb/CuNi structures

  23. Investigation of the morphology of S/F nanostructures (AFM, XRD,RBS) AFM scan of Nb/CuNi( S15) RBS-measurements

  24. Si Cap CuNi Niob Si Buffer Substrate 3.Re-entrante behavior of superconductivity in Nb/CuNi structures IEEIT

  25. Superconducting transitions of Nb/CuNi bilayers

  26. Experimental observation of the re-entrant superconductivity in Nb/Cu41Ni59bilayers (V.I. Zdravkov et al., PRL 97, 057004, 2006) Non monotonous Tc (dF) (dNb≈14.1, and 8.3 nm), and re-entrant Tc (dF) behavior for dNb≈7.3 nm < ξs  8 nm. Measured down to 40 mK (dilution He3-He4)

  27. First experimental observation of the double re-entrant superconductivity in Nb/Cu41Ni59bilayers (A.S. Sidorenko et al.,. Quasi-One-Dimensional Fulde-Ferrell-Larkin-Ovchinnikov-Like State in Nb/Cu41Ni59 Bilayers. Pisma ZhETF, v.90, 149 (2009).) Non monotonous Tc (dF) (dNb≈14.1, and 7.8 nm), and re-entrant Tc (dF) behavior for dNb≈6.2nm < ξs  8 nm. the next islandof superconductivity is possible to observe in the range dCuNi ≈ 44-56 nm.

  28. Solid curves are calculated based on the procedure: LR. Tagirov, Phys. C 307 (1998) 145 - with the common set of parameters for all curves : ξS= 10.2 nm NFvF/NSvS= 0.17, TF= 0.845, lF/ξF0 =1.2 (closer to the “clean” case), ξF0= 8.6 nm, lF  ≈ 10.3 nm – from <ρFlF> ≈ 2.5·10-5 μΩ·cm2, using measured ρF ≈ 25 μΩ·cm

  29. AP IEEIT SP SAP N P

  30. AP S/F spin-switch IEEIT P

  31. 4. CONCLUSIONS 1. Novel technology of SF hybrids production (suitable for spintronics) is developed 2. The first pronounced observation of the re-entrant and double re-entrant superconductivity in S/F bilayers with thickness of the superconducting layer ds<ξs 10 nm is announced. 3. The experimentally-theoretical base for the spintronic device design is developed. Thank you for attention

  32. Workshop Karlsruhe, 13-17 July 2008 Magnetic properties Ferromagnetic ordering and spinglass-like behavior of magnetization for sample 34 from batch S15

  33. Workshop Karlsruhe, 13-17 July 2008 IEEIT ln t = (½) – Re( ½ +p /t ) FS ,

  34. Workshop Karlsruhe, 13-17 July 2008 Si Cap Nb Si Buffer Substr. 2. Auger measurements of Nb films IEEIT

  35. Si CuNi Nb Si Nb Substrate (Si) Sample preparation- Novel Technology :Sidorenko A.S., Zdravkov V.I., “Instalaţie pentru obţinere peliculelor conductoare”, Patent of RM №4831 from 28 June 2006. • Equidistant cutting of long sample (~80 mm) along the wedge produces a batch of samples:

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