Post on 23-Feb-2016
description
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.