Pseudogap effects on the ferromagnetic Pseudogap effects on the ferromagnetic transition of transition of
YBaYBa22CuCu33OOyy and SrRuOand SrRuO33 bilayersbilayersoror
Do preDo pre--formed pairs exist above Tformed pairs exist above Tc c ??
Gil Aharonovich and Gad Koren.Technion - Israel Institute of Technology
In collaboration with Emil Polturak
Outline
• Background -the pseudogap and the pre-formed pairs scenario
• Motivation & Methodology of how to design the experiment
• Results and discussion • Conclusions
T* from R vs. T measurementsAndo & Segawa, PRL, 88, 167005 (2002)
Wuyts, Moshchalkov, and Bruynseraede PRB, 53 9418 (1996)
T* on the phase diagram
T*
Motivation To look for a signature of pre-formed pairsvia a proximity effect in S/F bilayers of YBa2Cu3Oy/SrRuO3 where the YBCO is in the pseudogap regime
For T<Tc S FStandard PE:
For Tc<T<T* PG F?PG/F PE:
Where F is the probe
As the ferromagnetic layer (F)we chose SrRuO3 (the “probe”)
0 50 100 150 200 250 300200
400
600
800
1000
1200
1400
100 110 120 130 140 150 160 170 180 190 200 210 2202
3
4
5
6
7
dR/d
T ( ΩΩ ΩΩ
/ K
)
T (K)
5nm SRO
BLR1004
SRO
R (
Ω)
T (K)
Show the dR/dT relation to dM/dT& sensitivity issues
00
1x10-7
2x10-72x10-7
3x10-7
4x10-74x10-7
5x10-7
6x10-76x10-7
100 110 120 130 140 150 160 170 180 190 200
0.00
0.01
0.02
0.03
0.04
dR/dT
dR
/dT
(Ω
/ Κ)
& |d
M/d
T| (
106 A
m2 )
T (K)
|dM/dT|*106
TP=144K
200 nm SRO film
<Z
-Mom
ent>
(A
m2 )
<Z-Moment>
Preparation of the bilayers and reference films
10nm c-axis YBCO
5 nm SrRuO3
(100) SrTiO3
Preparation of a bilayer and its reference film on the same wafer
by the use of a shadow mask
10nm c-axis YBCO
5 nm SrRuO3
(100) SrTiO3
Simple patterning & contacts config.
STO (100)
SRO SRO
YBCO
Io
IoV
V
IoIo
STO (100)
SRO SRO
YBCO
STO (100)
SRO SRO
YBCO
STO (100)
SRO SRO
YBCO
T*
Where did we work on the P.D. and why?
For YBa2Cu3Oy :
T*
TCurie of SrRuO3 is 150 K
For the TC= 30 K phase T*~ 230 K
For the TC=90 K phase T*~ 110 K
For the TC =60 K phase T*~ 180 K
Results at different doping levels
0 30 60 90 120 150 180 210 240 270 3000
200
400
600
800
1000
1200
1400
data on 10x10 mm2 films 5nm SRO
7.5nm c-axis YBCO / 5nm SRO / (100) STO Bilayer 30K Bilayer 60K Bilayer 90K
R (
Ω)
T (K)
20 40 60 80 100 120 140 160 180 200 2200
2
4
6
TP=137 K
dR/d
T (
Ω /
K)
T(K)
5nm SRO filmSame bilayer with different T
C
7.5 nm YBCO on 5 nm SRO BL T
c= 30K
BL Tc=60K
BL Tc=90K
BL 60K norm. BL 90K norm.
Temperature derivatives of the Resistance
• A 7.5 nm thick YBCO layer is too thin to shift the Tp of SRO
10nm YBCO on 5nm SROTest the contributions of the separate layers
And the interaction between them
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1.0
1.5
2.0
2.5
3.0
3.5 pseudogapT*~170 -200 K
dR/d
T (
Ω /
K)
T (K)
5 nm SRO 10 nm YBCO norm. calculated BL norm. measured BL
Bilayers with the 30, 60 and 90 K YBCO
0 100 200 3000
500
1000
1500
100 110 120 130 140 150 160 170 180 190 200
1
2
3
4
5
6
7
6 K
BL: 10nm YBCO/5nm SRO
dR/d
T(Ω
/K)
T(K)
BL 30 K BL 60 K BL 90 K 5 nm SRO
BL 30 K BL 60 K BL 90 K SRO
R (
Ω)
T (K)
A large Tpshiftwhen theYBCO is at 30 & 60 K
The 90 K phase Peak is toobroad andsmall todetermine Tp, But we havebetter data
A BL & a reference layer on the same wafer
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4
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8
STO (100)
SRO SRO
YBCO
Io
Io
VV
IoIo
STO (100)
SRO SRO
YBCO
STO (100)
SRO SRO
YBCO
STO (100)
SRO SRO
YBCO
Io
Io
VV
IoIo
Nor
mal
ized
dR
/dT
(Ω /
K)
T (K)
SRO 10nm YBCO (60K phase)/ 5nm SRO
6 K
• Are the conjectured preformed pairs injected into the SRO layer lowering its Tp ??
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250
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750
1000
1250
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3
4
5
6
7 TP=139K
Nor
mal
ized
dR
/dT
(Ω
/ K
)
T (K)
5nm SRO 10nm YBCO (90K)/ 5nm SRO 10nm LSCO 12% Sr/ 5nm SRO
SRO YBCO/SRO LSCO/SRO
R (
Ω)
T (K)
Control experiments in BL with cupratesout of the pseudogap regime (T*<120 K)
• No shift of Tpfor both YBCO & LSCO in this case
No effect by the injection of normal electrons from the SC above T*into the SRO
A control experiment in a bilayer with an antiferromagnet (Cr)
10 nm Cr/ 5 nm SRO1. Injection ofelectrons with opposite spinsinto the SROleads to only a 2 K shift down of Tp
0 50 100 150
0
200
400
600
800
1000
100 120 140 160 180 200
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4
5
6
7
8
2 KN
orm
aliz
ed d
R/d
T (
Ω /
K)
T(K)
5nm SRO ZFC 10nm Cr/ 5nm SRO ZFC
10nm Cr/ 5nm SRO
5nm SRO
R (
Ω)
T (K)
2. An inverse PE can lead to lossof itinerant electrons in the SRO, thus lowering its Tp
Comparison of the main results
• Large Tp shifts – only when the YBCO is in the PG regime!• A small Tp shift – by injection of electrons with opposite spins• Thus only the injection of correlated electrons with zero spin
yields a large effect – these might be the preformed pairs
100 120 140 160 180 200
2
4
6
8
STO (100)
SRO SRO
YBCO
Io
Io
VV
IoIo
STO (100)
SRO SRO
YBCO
STO (100)
SRO SRO
YBCO
STO (100)
SRO SRO
YBCO
Io
Io
VV
IoIo
Nor
mal
ized
dR
/dT
(Ω /
K)
T (K)
SRO 10nm YBCO (60K phase)/ 5nm SRO
6 K
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250
500
750
1000
1250
100 110 120 130 140 150 160 170 180 190 2002
3
4
5
6
7 TP=139K
Nor
mal
ized
dR
/dT
(Ω
/ K
)
T (K)
5nm SRO 10nm YBCO (90K)/ 5nm SRO 10nm LSCO 12% Sr/ 5nm SRO
SRO YBCO/SRO LSCO/SRO
R (
Ω)
T (K)
0 50 100 150
0
200
400
600
800
1000
100 120 140 160 180 200
3
4
5
6
7
8
2 K
Nor
mal
ized
dR
/dT
(Ω
/ K
)
T(K)
5nm SRO ZFC 10nm Cr/ 5nm SRO ZFC
10nm Cr/ 5nm SRO
5nm SRO
R (
Ω)
T (K)
AF FN F
T*<120K
PG F?
T*>170
∆Tp~ 0 ∆Tp~ 6 K ∆Tp~ 2 K
Conclusions
• Large Tp shifts –necessitates correlated electrons injection
• This is consistent with the preformed pairs scenario, but is not a definitive proof of their existence
• But…
• If it looks like a duck, sounds like a duck and walks like a duck, it is a duck!!