Upload
theta
View
36
Download
0
Tags:
Embed Size (px)
DESCRIPTION
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 - PowerPoint PPT Presentation
Citation preview
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.OboznovUniversität Augsburg, Germany - M. Schreck, G.Obermeier, C. Müller, S. Horn, R. Tidecks
Karlsruhe Institute of Technology, Germany – H.Hahn, E.NoldMoscow State University, Russia – M.Yu. Kupriyanov
Mesoscopic and strongly correlated systemsChernogolovka, 11-16.10. 2009
O U T L I N E
1. Coexistence of S-F, FFLO state2. Proximity effect in S/F layers, quasi-1D FFLO3. Novel technology --> Re-entrant superconductivity 4. Conclusions
ESF Exploratory Workshop Paestum (Salerno), Italy, 20-21 June 2008
kF
min kF
max
k
E
EF
Eexc
-kF
m ax
+kFm ax
+k F
min
-kFm i n
= -kF 1
= +kF 2
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).
Exchange field splits
conduction band of ferromagnet
Singlet pairs in a ferromagnet
- non uniform FFLO pairing
Eex/0 FFLO state:Strict limitation: 0,71 0 < Eex < 0,76 0
Eex ~ 0.1-1 eV0 ~ 0.001 eV
S
S
F
N
x
x
F
De Gennes, Rev.Mod.Phys.36 (1964)225
In F-layer: nonzero pairing momentum , q0 ~
Eex ≠ 0, FFLO-like state
A. Buzdin, Z. Radović, PR B38 (1988) 2388
2) FFLO-like 1D-stateProximity-effect:
FF oscillates on magnetic coherence length, 2 = F = ħvF/Eex
and relaxes on decay length, 1= lF
)cos( 21 xeF x
F
SF Vacuum
dF
Interference of Pairing FunctionIn F-layer:Fabry-Perot interferometeranalogy
12cos( )x
FF e x
Z. Radovich et al, PRB 44, 759 (1991)
Oscillations of superconducting Tc as a function of the ferromagnetic layer thickness in
multilayers
π-phase
0-phase
ln t = (½) – Re( ½ + /t )
dF/F
non monotonous TC(dF) for S/F : t=Tc/TcS
A lot of attempts – controversial results:
Nb/Gd Ch.Strunk, PRB 49 (1994) 4053 (MBE) – no oscil.J.Jiang, PRL 74 (1995) 314 (dc-magnetron) – oscil.
Nb/Fe G.Verbank, PRB 57 (1998) 6029 (MBE) – no oscil. 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.
A. Buzdin, Z. Radović, PR B38 (1988) 2388
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
20-70 nm5-8nm
Nb/Ni samples magnetron sputtering
XRD RBS
Thickness measurement accuracy: dNi ± 0.03 nmRoughness: rms < 0.3 nm
dF/F
TC oscillation in Nb/Ni bilayer: quasi-1D FFLO state
A. Sidorenko, V. Zdravkov, A.Prepelitsa et al., Ann. Phys. 12 (2003) 37.
(Curves 1-5: variable interface transparency, Tm= 5, 2.5, 1.25, 0.5, 0.25)
L. R. Tagirov, Phys. C 307 (1998) 145
dF/F
3). Re-entrant superconductivity
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
Calculation for S/F sandwich – oscillations TC up to re-entrance:
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
1) dS, / S ~ 1 dS, ~ 10 nm
0 10 20 30 40 500
2
4
6
8
Tc (dNb)
dCuNi56 nm
Experiment Calculation
Tc
(K)
dNb (nm)
2) alloy Cu0.41 Ni0.59 ξF = ħvF/Eex ~ 8 nm
(allows larger thicknesses dF of about 5-10 nm )
Our pilot experiments with Nb/Cu0.41Ni0.59
The necessity of technology development for ultra-thin S and F layers preparation
Sample preparation- Novel Technology :Sidorenko A.S., Zdravkov V.I., “Instalaţie pentru obţinere peliculelor conductoare”,
Patent of RM №3135 from 31.08 2006.
• DC magnetron sputtering
a) high deposition rate (4 nm/s)
b) moving Nb target(precisely constant S-layer thickness)
Nb-target with holder:
moving target
1. Superconducting properties of prepared Nb films
Critical temperatures for Nb
films with thickness 5.5-14 nm
6,0 6,4 6,8 7,2 7,6 8,0
0
2
4
6
8
10
12
14
16
18
, O
hm *
cm
T, K
Nb, thickness: d(Nb)=6,8 nm
Thickness, (nm)
Critical temperature ,Tc (К)
Nb 5,5 5,7
10 7,4
28 8,25
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.
CuNi
Nb
Substrate (Si)Substrate (Si)
Si
SiNb
Si-Substrat
Si-Cap
CuNi
Nb
Si-Buffer
Nb/CuNi
22#18
dCuNi= 14.1nm
dNb = 6nm
2. TEM of Nb/CuNi structures
Si-Substrate
CuNi wedge
Niobium
Silicon cap and buffer layers
Silicon substrate
50 µ
m
50 µ m
Surface
Si Substrate
Nb
Si-oxide
Si
SEM 2 Crater Edge
SEM measurements of Nb film
2. Investigation of the morphology of prepared Nb films and S/F nanostructures (AFM, XRD, SEM, RBS, Auger)
Si
N
Si
Sub
S23_12_1004.sem: SEM: SEM 2 crateredge FZK IMF1
07 Dec 3 10.0 keV 0 FATSEM/Full
20 µ
m
50 µ m
Si Substrate
Nb
CuNi
Surface Si-oxid
Si
SEM 2 Crater Edge
200
µm
200 µm
SEM 1 Crater
2. SEM measurements of Nb/CuNi structures
Workshop Karlsruhe, 13-17 July 2008
S23_12_1001.pro: SEM 1 Profil FZK IMF1
07 Dec 3 10.0 keV 0 FRR 9.7957e+001 maxNb1/Full (Binom3)
0 20 40 60 80 100 120 1400
10
20
30
40
50
60
70
80
90
100S23_12_1001.pro
Sputter Time (min) Rate 1nm/min Si-ox.
Ato
mic
Con
cent
ratio
n (%
)
ONbSi
CuNiNC
O
Si
O
Nb
Cu
Ni
NC
Nb
Si
2. Auger measurements of Nb/CuNi structures
Investigation of the morphology of S/F nanostructures (AFM, XRD,RBS)
0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32 340
5
10
15
20
25
30
35
0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32 340
5
10
15
20
25
30
35
0
566064
Thi
ckne
ss o
f N
b an
d C
uNi (
nm)
Sample #
Nb
CuNi
Ni content
CuNi wedge
Niobium
Silicon cap and buffer layers
Silicon substrate
Ni c
once
ntra
tion
in C
uNi (
%)
S15
RBS-measurementsAFM scan of Nb/CuNi ( S15)
3. Re-entrante behavior of superconductivity in Nb/CuNi structures
Si Cap
Niob
CuNi
Si Buffer
Substrate
Superconducting transitions of Nb/CuNi bilayers
0 1 2 3 4 5 6 7 8
0,0
0,2
0,4
0,6
0,8
1,0
0,0
0,2
0,4
0,6
0,8
1,0
dNb7.3 nm
#
sample dCuNi
[nm]
———————— #04 1.0 #06 1.6 #07 2.6 #09 5.0 #14 9.5 #16 11.5 #20 16.7 #22 19.3 #29 30.3
R/R
n
T (K)
#S15
sample dCuNi[nm]
———————— #03 0.7 #06 2.3 #10 6.5 #14 11.4 #16 12.8 #18 17.2 #25 28.2 #31 35.6
dNb8.3 nm
R/R
nS16
Experimental observation of the re-entrant superconductivity in Nb/Cu41Ni59 bilayers (V.I. Zdravkov et al., PRL 97, 057004, 2006)
Measured down to 40 mK (dilution He3-He4)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.
First experimental observation of the double re-entrant superconductivity
in Nb/Cu41Ni59 bilayers (A.S. Sidorenko et al.,. Quasi-One-Dimensional
Fulde-Ferrell-Larkin-Ovchinnikov-Like State
in Nb/Cu41Ni59 Bilayers. Pisma ZhETF, v.90, 149 (2009).)
the next island of superconductivity is possible to observe in the range dCuNi ≈ 44-56 nm.
Non monotonous Tc (dF) (dNb≈14.1, and 7.8 nm),
and re-entrant Tc (dF) behavior
for dNb≈6.2nm < ξs 8 nm.
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
SP SAP N
APP
P
AP
0,0
0,2
0,4
0,6
0,8
1,0
R/R
n
BEXTERNAL
B
SWITCH
Superconducting state
Normal state
S/F spin-switch
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.
Ferromagnetic ordering and spinglass-like behavior of magnetization for sample 34 from batch S15
Magnetic properties
0
5,0x10-7
1,0x10-6
1,5x10-6
2,0x10-6
2,5x10-6
3,0x10-6
3,5x10-6
Mmol
= 1.000 g/mol
m = 30.72 mg
CuNi S15-34
(e
mu
/mo
l)
0 100 2000
1000000
2000000
3000000
4000000
H = 100 Oe
1/
(mo
l/em
u)
T (K)
Workshop Karlsruhe, 13-17 July 2008
Workshop Karlsruhe, 13-17 July 2008
SS dk S
M
F S ,
FFFFM
M llI
D 6,13
22
4
2
0
tanh( )tan ,
2 1 / (2 / ) tanh( )S BCSF F F F
S S S F F F F F
dN v k d
N v i l T k d
21 22
/ / ,S Sd
0 0/ 1 / .F F F Fk i l
ln t = (½) – Re( ½ +p /t )
nb7_1003.pro: SEM 1 full area x20000 profile 2 FZK IMF1
07 Nov 30 10.0 keV 0 FRR 2.7738e+001 maxSi1/Full (Binom3)
0 10 20 30 40 50 60 70 80 900
10
20
30
40
50
60
70
80
90
100nb7_1003.pro
Sputter Depth (nm)
Ato
mic
Con
cent
ratio
n (%
)
Si1.ls1
O1.ls1
C1.ls1
O
Si
O
SiNb
C
Nb1.ls1
Nb
C
2. Auger measurements of Nb films
Si Cap
Nb
Si Buffer
Substr.
Workshop Karlsruhe, 13-17 July 2008
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:
CuNi
Nb
Substrate (Si)Substrate (Si)
Si
SiNb