Ph.D. Amit KanigelPh.D. Rinat OferMSc. Yuval LubashevskyPh.D. Eran AmitPh.D. Gil Drachuck

CollaboratorsG. Bazalitski-TechnionA. Knizhnik-TechnionJ. Lord-ISISA. Amato-PSIO. Chmaissem-ANLB. Wilds-ILLP. Lemmens-BraunschweigE. Razzoli & M. Shi -PSI

A magnetic analog of the isotope effect in cupratesAmit Keren

What is superconductivity?

0 10 20 30 40 50 60-18-16-14-12-10-8-6-4-202

M (e

mu

10-4

)

Temperature (K)

Tc

Magnetization Resistivity

0 20 40 60 80 1000.000

0.005

0.010

0.015

R (m

Ohm

-cm

)

Temperature (K)

Tc

Superconductivity

Fermions Attraction

1/ 2cT M

BCS

Isotope effect

2Cu3Cu

2Cu3Cu ~15%

Y

BaCu

O

What are HTSC’s? Y1Ba2Cu3Oy

< , >i j

i j

H J S S

B. Serin et al., Phys. Rev. 86, 162 (1952).

C. A. Reynolds et. al., Phys. Rev. 84, 691 (1950).

E. Maxwell et al., Phys. Rev. 95, 333 (1954).

• Maximum 4% variation of Tc in Sn.• The (0,0) point is important.• The is not applicable for different materials. 1/2

cT M

The Isotope Effect

Our motivation

We would like to change J, with no other structural changes, and see the effect on Tc.

• We will know that we changed J if TN changes.• Experimentally this is difficult but not inconceivable.

Tg

T*

TN

Tc

T

P

AFM

SG

PG

SC

To make a magnetic measurement equivalent of the isotope effect.

• YBa2Cu3Oy structure.

• Tetragonal at all x and y.

• 2 planes per unit cell.

• Over doping is possible.

• Tc variation of 30%.

• Valance Ca=Ba=2, La=3.

• Similar level of disorder.

6.80 6.85 6.90 6.95 7.00 7.05 7.10 7.15 7.20 7.250

20

40

60

80

(CaxLa1-x)(Ba1.75-xLa0.25+x)Cu3Oy

y

X=0.1 X=0.2 X=0.3 X=0.4

T c(K)

CLBLCO; Our Model Compound

CLBLCO allows Tcmax variations, with minimal structural changes.

Goldschmidt et al., Phys. Rev. B 48, 532 1993

The role of x (CaxLa1-x)(Ba1.75-xLa0.25+x)Cu3Oy

• Positive change is moving out with increasing x. • This alters the oxygen position.

+

+

Structural variation between families

4.0

4.5

5.0

5.5

6.0

6.5

6.4 6.6 6.8 7.0 7.23.87

3.88

3.89

3.90

3.91

3.92

Buc

klin

g an

gle

(deg

.)

y

a [A

]

x=0.1 x=0.2 x=0.3 x=0.4 Cu Cu

Oq

a

(CaxLa1-x)(Ba1.75-xLa0.25+x)Cu3Oy

• Buckling angle and distance decreases with increasing x.

J variations between families.

6.4 6.6 6.8 7.0 7.2 7.40.98

1.00

1.02

1.04

1.06

1.08

1.10

1.12

1.14

J~co

s2 (q)/a

14 (

a.u.

)

y

x=0.1 x=0.2 x=0.3 x=0.4

(CaxLa1-x)(Ba1.75-xLa0.25+x)Cu3Oy

< , >

2

14

cos

i ji j

H J

Ja

q

S S

• J increases with x mainly due to decreasing buckling angle.

• We will verify this by TN and Tg measurements using mSR.

Principals of mSR

Asymmetry = (F-B)/(F+B) Pz(t).

Asy

mm

etry

Time

Uniform FieldRandom Field

Time

Principals of mSR

0 200 400 6001500

2000

2500

3000

Cou

nts

Bins0 200 400 600

1500

2000

2500

3000

Cou

nts

Bins

• There are oscillations in the ordered phase but not in the spin glass phase.

Raw Zero Field mSR Data

0 2 4 6 8 100.00

0.05

0.10

0.15

0.20

0.25

Time msec)

(a)

T(K)= 40.2 7.4 3.8 2.1 0.37

Asy

mm

etry

Tc=33.1K

0 2 4 6 8 100.10

0.15

0.20

0.25

0.30

Asy

mm

etry

T(K)=381

379

378

377

375303

Tg

T*

TN

Tc

T

P

Phase Diagram of (CaxLa1-x)(Ba1.75-xLa0.25+x)Cu3Oy

6.4 6.6 6.8 7.0 7.20

20

40

60

80

180240300360420 TN,Tg Tc x

0.10.20.30.4

T N, g

, C (

K)

y

TC

Tg

TN

• The family with the highest Tcmax has the highest TN at zero doping.