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

60 80 100 120 140 160 180 200 220 240

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

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

• Are the conjectured preformed pairs injected into the SRO layer lowering its Tp ??

0 100 200 3000

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)

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

3

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

0 100 200 3000

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!!