スライド 1

Systematic As-NMR study on iron
oxpnictides F-doped LaFeAsO
Kitaoka Laboratory
Hiroki Yamashita
Reference : Y. Nakai et al., J. Phys. Soc. Jpn 77, 073701 (2008)
Y. Nakai et al., cond-mat/arXiv:0810.3569v1 (2008)
Contents
Introduction
・ history of superconductivity.
・ Fe-based oxypnictide compound.
・ Motivation.
NMR measurement
Experimental results
Summary
History of superconductivity
1911
200
High-Tc cuprate
metal
Iron-based system
Hg-Ba-Ca-Cu-O
Transition temperature (K)
163
150
（at a suitable pressure
）
Hg-Ba-Ca-Cu-O
Tl-Ba-Ca-Cu-O
Bi-Sr-Ca-Cu-O
100
Y-Ba-Cu-O
SmO0.9F0.11FeAs
50
Pb
Hg
0
1900
La-Ba-Cu-O
Nb
NbC
1920
1940
NbN
MgB
2
NbGe
1960
Year
1980
1957
BCS theory
(Bardeen Cooper Schrieffer)
1986
77 nitrogen temperature
BCS limit
Superconductivity was
discovered .
LaO0.89F0.11FeAs
LaOFeP
2000
2020
High-Tc cuprate was
discovered .
2006
Iron-based layered
oxypnictide .
cuprate : 銅酸化物
Iron-based oxpnictide compound
Phase diagram
LaFeAs(O1-xFx)
160
Charge reservoir
layer
LaFeAsO1-xFx
140
FeAs layer
e-
Charge reservoir
layer
TN , TC(K)
120
100
TN from μSR
80
40
20
0
0.00
F
Electron dope
TC from μSR
AFM
60
??
0.04
SC
0.08
0.12
0.16
0.20
Nominal F content x
(O2-→F-)
H. Luetkens et al., arXiv:0806.3533v1
・ Superconducting transition relates to a magnetic instability ??
AFM:反強磁性
SC:超伝導
Motivation
x = 0 sample : mother material
LaFeAs(O1-xFx)
x = 0.04 sample locates near the
boundary between the AFM and SC phase.
x = 0.07 sample : under-doped region
160
LaFeAsO1-xFx
140
x = 0.14 sample : over-doped region
120
TN , TC(K)
x = 0.11 sample : optimally-doped region
100
TN from μSR
80
TC from μSR
AFM
60
40
20
0
0.00
SC
0.04
0.08
0.12
0.16
0.20
Nominal F content x
H. Luetkens et al., arXiv:0806.3533v1
We show systematic As-NMR stud
on these samples.
NMR measurement(1)
Example As : I = 3/2
m= -3/2
m=±3/2
Energy
Energy
=
m= -1/2
=
m= +1/2
=
m=±1/2
m= +3/2
Zeeman splitting
Quadrupole splitting
m= -3/2
HZ>>HQ
Energy
H = H Z + HQ
=
=
=
m= -1/2
m= +1/2
m= +3/2
NMR measurement(2)
m= -3/2
Energy
=
=
=
m= -1/2
m= +1/2
m= +3/2
Echo Intensity
second-order perturbation into the calculation
E
1
1

2
2
1
1

2
2

1
3

2
2
Spin-lattice relaxation time T1
E
external magnetic field
E
m=-1/2
m=1/2
m=-1/2
2Δ
m=1/2
E
Zeeman splitting
Excitation
1
T5
T1
relaxation
E
m=-1/2
conduction electron
m=1/2
1/T1 proportional to density of states.
1
T3
T1


1
 e k bT
T1
Experimental result(1)
LaFeAsO
ρ(mΩ・cm)
9
TN
6
3
The x=0 sample does not
exhibit superconductivity.
0
1/T1(s-1)
12
6
0
0
50
200
150
100
Temperature(K)
250
300
＊TN : antiferromagnetic transition temperature
LaFeAsO is an itinerant
antiferromagnet with
TN～142K.
Experimental result(3)
X=0.14 sample does not exhibit
superconductivity in H～9.89T.
Recent theoretical
1/T1∝T3
Shape of gap
ARPES measurement
Penetration depth measurement
1/T1∝T3
inconsistent
Line node
Nodeless SC gap??
Fully gaped S± state
with impurity effect
Y. Nagai, et al., arXiv:0809.1197 (2008)
H. Ding, et al., Europhys. Lett. 83, 47001 (2008).
T. Kondo, et al., Phys. Rev. Lett. 101, 147003 (2008).
K. Hashimoto, et al., arXiv:0806.3149 (2008).
Experimental result(2)
LaFeAs(O0.96F0.04)
nonmetallic behavior
We did not find a huge
increase of 1/T1.
The magnetic anomaly becomes
weakened upon F-doping.
TN
The line width increases
gradually below TN.
1/T1(s-1)
12
6
0
0
＊TN : antiferromagnetic transition temperature
＊TC : superconducting transition temperature
50
100 150 200 250 300
Temperature(K)
▲LaFeAsO 1/T1 vs T
Experimental result(4)
At the x=0.07 sample ,
(T1T)-1 decrease rapidly.
T* is not ascribed to
a magnetic anomaly.
Pseudogap behavior
At x = 0.11 and x = 0.14 sample,
pseudogap behavior is more pronounced.
La2-xSrxCuO4
Pseudogap behavior is more pronounced
in the underdope region.
Summary
・Upon F-doping significant AFM fluctuations observed
at x=0.04 are suppressed,and pseudogap behavior appears
At x=0.11 and x=0.14.
・With existing experimental
results,we have developed a
phase diagram of LaFeAs(O1-xFx) .

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