A magnetic analog of the isotope effect in cuprates

micefunctionalΠολεοδομικά Έργα

15 Νοε 2013 (πριν από 3 χρόνια και 8 μήνες)

98 εμφανίσεις

Ph.D. Amit Kanigel

Ph.D. Rinat Ofer

MSc
. Yuval
Lubashevsky

Ph.D. Eran Amit

Ph.D. Gil Drachuck

Collaborators

G.
Bazalitski
-
Technion

A.
Knizhnik
-
Technion

J. Lord
-
ISIS

A.
Amato
-
PSI

O.
Chmaissem
-
ANL

A.
Wilds
-
ILL

P
.
Lemmens
-
Braunschweig

E.
Razzoli

& M. Shi
-
PSI

A
magnetic analog
of the
isotope effect
in
cuprates

Amit Keren

What is superconductivity?

0
10
20
30
40
50
60
-18
-16
-14
-12
-10
-8
-6
-4
-2
0
2


M (emu
´
10
-4
)
Temperature (K)
T
c
Magnetization

Resistivity

0
20
40
60
80
100
0.000
0.005
0.010
0.015


R (mOhm-cm)
Temperature (K)
T
c
Superconductivity

Fermions

Attraction

1/2
c
T M


BCS

Isotope effect

2

Cu
3

Cu
2

Cu
3

Cu
~15%

Y

Ba

Cu

O

What are HTSC’s?

Y
1
Ba
2
Cu
3
O
y

<,>
i j
i j
H J


SS
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
T
c

in
Sn
.



The (0,0) point is important.



The
is
not applicable for different materials.

1/2
c
T M


The Isotope Effect

Our motivation

We would like to change
J,

with no other structural changes
, and see
the effect on
T
c
.



We will know that we changed
J

if
T
N

changes.



Experimentally this is difficult but not inconceivable.

T
g
T*
T
N
T
c
T
P
AFM

SG

PG

SC

To make a magnetic measurement equivalent of the isotope effect.



YBa
2
Cu
3
O
y

structure.




Tetragonal at all x and y.




2 planes per unit cell.




Over doping is possible.




T
c

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
7.25
0
20
40
60
80
(Ca
x
La
1-x
)(Ba
1.75-x
La
0.25+x
)Cu
3
O
y
y


X=0.1
X=0.2
X=0.3
X=0.4
T
c
(K)
CLBLCO; Our Model Compound

CLBLCO allows
T
c
max


variations,
with minimal structural changes.

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

The role of
x

(Ca
x
La
1
-
x
)(Ba
1.75
-
x
La
0.25
+x
)Cu
3
O
y



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
7.2
3.87
3.88
3.89
3.90
3.91
3.92


Buckling angle (deg.)

y
a [A]



x=0.1

x=0.2

x=0.3

x=0.4
Cu

Cu

O

q

a

(Ca
x
La
1
-
x
)(Ba
1.75
-
x
La
0.25+x
)Cu
3
O
y



Buckling angle and distance decreases with increasing x.

J

variations between families.

6.4
6.6
6.8
7.0
7.2
7.4
0.98
1.00
1.02
1.04
1.06
1.08
1.10
1.12
1.14


J~cos
2
(
q
)/a
14
(a.u.)
y

x=0.1

x=0.2

x=0.3

x=0.4
(Ca
x
La
1
-
x
)(Ba
1.75
-
x
La
0.25
+x
)Cu
3
O
y

<,>
2
14
cos
i j
i j
H J
J
a
q



S S

J

increases with
x

mainly
due to decreasing
buckling angle
.




We will verify this by
T
N


and
T
g

measurements using
m
SR
.

Principals of
m
SR

Asymmetry = (F
-
B)/(F+B)


P
z
(t).

Time

Uniform Field

Random Field

Time

Principals of
m
SR

0
200
400
600
1500
2000
2500
3000


Counts
Bins
0
200
400
600
1500
2000
2500
3000


Counts
Bins



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



Raw Zero Field
m
SR

Data

0
2
4
6
8
10
0.00
0.05
0.10
0.15
0.20
0.25


Time
(
m
sec)
(a)
T(K)=
40.2
7.4
3.8
2.1
0.37
Asymmetry
T
c
=33.1K
0
2
4
6
8
10
0.10
0.15
0.20
0.25
0.30


Asymmetry
T(K)=381
379
378
377
375
303
T
g
T*
T
N
T
c
T
P
Phase
Diagram of
(Ca
x
La
1
-
x
)(Ba
1.75
-
x
La
0.25
+x
)Cu
3
O
y

6.4
6.6
6.8
7.0
7.2
0
20
40
60
80
180
240
300
360
420
T
N
,T
g
T
c
x
0.1
0.2
0.3
0.4
T
N, g, C
(K)
y
T
C
T
g
T
N


The
family with
the highest
T
c
max

has the highest
T
N


at zero doping
.