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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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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

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


Double re entrant superconductivity in sf hybrids a s sidorenko

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


Double re entrant superconductivity in sf hybrids a s sidorenko

1) FFLO state

P. Fulde, R. A. FerrellPhys.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


Double re entrant superconductivity in sf hybrids a s sidorenko

FFLO state:

Eex/0

Strict limitation: 0,71 0 < Eex < 0,76 0

Eex ~ 0.1-1 eV

0 ~ 0.001 eV


Double re entrant superconductivity in sf hybrids a s sidorenko

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


Double re entrant superconductivity in sf hybrids a s sidorenko

Interference of Pairing Function

In F-layer:

Fabry-Perot interferometer

analogy

F

Vacuum

S

dF


Double re entrant superconductivity in sf hybrids a s sidorenko

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


Double re entrant superconductivity in sf hybrids a s sidorenko

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/FeG.Verbank,PRB57 (1998) 6029 (MBE) – nooscil. I.Garifullin, PRB 55 (1997) 8945 (dc-magnetron) - oscil.

Nb/CuMnC.Attanasio, PRB 57 (1998) 14411 (dc-magnetron) – oscil.

Nb/CuNi V.Ryazanov et al., JETP Lett. 77 (2003) 43(dc-magnetron) – oscil.


Double re entrant superconductivity in sf hybrids a s sidorenko

  • 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


Double re entrant superconductivity in sf hybrids a s sidorenko

magnetron sputtering

Nb/Ni samples

5-8nm

20-70 nm


Double re entrant superconductivity in sf hybrids a s sidorenko

XRD

RBS

Thickness measurement accuracy: dNi ± 0.03 nm

Roughness: rms < 0.3 nm


Double re entrant superconductivity in sf hybrids a s sidorenko

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)


Double re entrant superconductivity in sf hybrids a s sidorenko

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


Double re entrant superconductivity in sf hybrids a s sidorenko

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


Double re entrant superconductivity in sf hybrids a s sidorenko

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


Double re entrant superconductivity in sf hybrids a s sidorenko

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:


Double re entrant superconductivity in sf hybrids a s sidorenko

1. Superconducting properties of prepared Nb films

IEEIT

Critical temperatures for Nb

films with thickness 5.5-14 nm


Double re entrant superconductivity in sf hybrids a s sidorenko

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.


Double re entrant superconductivity in sf hybrids a s sidorenko

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


Double re entrant superconductivity in sf hybrids a s sidorenko

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


Double re entrant superconductivity in sf hybrids a s sidorenko

Workshop

Karlsruhe, 13-17 July 2008

2. SEM measurements of Nb/CuNi structures

IEEIT


Double re entrant superconductivity in sf hybrids a s sidorenko

IEEIT

2. Auger measurements of Nb/CuNi structures


Double re entrant superconductivity in sf hybrids a s sidorenko

Investigation of the morphology of S/F nanostructures (AFM, XRD,RBS)

AFM scan of Nb/CuNi( S15)

RBS-measurements


Double re entrant superconductivity in sf hybrids a s sidorenko

Si Cap

CuNi

Niob

Si Buffer

Substrate

3.Re-entrante behavior of superconductivity

in Nb/CuNi structures

IEEIT


Double re entrant superconductivity in sf hybrids a s sidorenko

Superconducting transitions of Nb/CuNi bilayers


Double re entrant superconductivity in sf hybrids a s sidorenko

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)


Double re entrant superconductivity in sf hybrids a s sidorenko

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.


Double re entrant superconductivity in sf hybrids a s sidorenko

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


Double re entrant superconductivity in sf hybrids a s sidorenko

AP

IEEIT

SP

SAP

N

P


Double re entrant superconductivity in sf hybrids a s sidorenko

AP

S/F spin-switch

IEEIT

P


Double re entrant superconductivity in sf hybrids a s sidorenko

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


Magnetic properties

Workshop

Karlsruhe, 13-17 July 2008

Magnetic properties

Ferromagnetic ordering and spinglass-like behavior of magnetization for sample

34 from batch S15


Double re entrant superconductivity in sf hybrids a s sidorenko

Workshop

Karlsruhe, 13-17 July 2008

IEEIT

ln t = (½) – Re( ½ +p /t )

FS ,


Double re entrant superconductivity in sf hybrids a s sidorenko

Workshop

Karlsruhe, 13-17 July 2008

Si Cap

Nb

Si Buffer

Substr.

2. Auger measurements of Nb films

IEEIT


Double re entrant superconductivity in sf hybrids a s sidorenko

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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