スライド 1

Superconductivity and Magnetism
in Iron-pnictide compounds
K. Kitagawa et al., to be published in J. Phys. Soc. Jpn (2008)
H. Chen et al., arXiv:0807.3950v1
Kitaoka Lab.
Nobukatsu TAMURA
Contents

Introduction

History of Superconductivity
 Crystal Structure of Fe-based system
 Superconductivity of “1-1-1-1”-system:LaFeAs(O1-xFx)
 Motivation

Experimental result of BaFe2As2 with “1-2-2”system
 “1-2-2” system
 Phase diagram of “1-2-2"
 75As-NMR spectra

Summary
system
History of Superconductivity
Transition temperature (K)
200
High-Tc cuprate
metal
Iron-based system
163
1911
Hg-Ba-Ca-Cu-O
（at a suitable pressure
）
150
Hg-Ba-Ca-Cu-O
Tl-Ba-Ca-Cu-O
Bi-Sr-Ca-Cu-O
100
77 nitrogen temperature
SmO0.9F0.11FAs
50
Pb
Hg
Nb
NbC
NbN
NbGe
MgB
LaO0.89F 0.11FAs
2
BaFe1.8Co0.2As2
LaOFeP
0
1900 1920 1940 1960 1980 2000 2020
Year
1986
High-Tc cuprate was
discovered
Y-Ba-Cu-O
La-Ba-Cu-O
Superconductivity was
discovered
2006
Fe - based system was
discovered
Crystal Structures of Fe-based system : FeAs layer
“1-1-1-1” structure
“1-2-2” structure
BaFe2As2
LaFeAsO
FeAs layer
Electron dope
(O2- → F-)
Tc~28K
(RE = Sm  50K)
Electron dope
(Ba2＋→K+)
Tc~37K
Superconductivity of LaFeAs(OF)
LaFeAs(O1-xFx)
(x is amount of dopes)
Resistivity
LaO layer
superconductivity
FeAs layer
LaO layer
Electron dope (O2- → F-)
Kamihara et al., JACS,2008
Resistivity go down to 0
below ~ 50K in LaFeAs(O1-xFx)
Phase diagram of “1-1-1-1” system
AFM
??
H. Luetkens et al., arXiv:0806.3533v1
・Superconductivity appears by doping carriers.
・ Superconducting transition relates to a magnetic instability ??.
Motivation

Carrier density and pressure dependence in Fe based system BaFe2As2.

Crystal structure and magnetic property in
BaFe2As2
 because it should play vital role for the
occurrence of superconductivity.
FeAs layer
BaFe2As2
“1-2-2” structure; Ba1−xKxFe2As2
Marianne Rotter et al., arXiv:0805.4630v1
H. Chen et al., arXiv:0807.3950v1
resistivity
x=0
BaFe2As2
FeAs layer
Ba layer
superconductivity
FeAs layer
x=0.4
spin susceptibility
x=0.4
Phase diagram of Ba1−xKxFe2As2
Ba1−xKxFe2As2
LaFeAs(O1-xFx)
AFM
??
??
H. Luetkens et al., arXiv:0806.3533v1
H. Chen et al., arXiv:0807.3950v1
The phase of “1-2-2”system resembles that of “1-1-1-1”
BaFe2As2 -pressure dependence resistivity
TN
Alireza et al., arXiv:0807.1896
Hideto Fukazawa et al., arXiv:0808.0718v1
arXiv:0808.0718v1
140
BaFe2As2
120
Tc [K]
100
AFM
80
60
40
20
SC?
BaFe2As2
3.8GPa
0
1
2
3
4
5
Pressure [GPa]
6
75As-NMR about
BaFe2As2
Ba1−xKxFe2As2
X=0
BaFe2As2 is “mother compound”.
??
If we would like to understand the magnetic property at superconducting and “??”phase,
It is important to know the structural and magnetic property in “mother compound”.
NMR~Nuclear Magnetic Resonance~
I = 3/2
H0
As
-3/2
±3/2,±1/2
=
Energy
＋
H z+ H Q
Hz
=
ℏγHz
=
H = H z = - ℏγHz・Iz
EFG：Electric Field Gradient
+1/2
+3/2
electric field gradient
Zeeman splitting
Ba2+
-1/2
γH=ω
nQ
As
Fe2+
nuclear quadrupole interaction
H Q = (nQ / 6) {3Iz’2 - I(I + 1)}
H
H0
the structural transition observed by 75As-NMR spectra
K. Kitagawa et al., to be published in J. Phys. Soc. Jpn (2008)
75As-NMR
∝ EFG
nQ are related to the electric field gradient (EFG) along each axis.
spectra
nQ
EFG
nQ
As
Tetragonal
Orthorhombic
the structural transition in 135K
a=b
a≠b
by X ray diffraction
Antiferromagnetic transition observed by75As-NMR spectra
K. Kitagawa et al., to be published in J. Phys. Soc. Jpn (2008)
Hint (T)
141K
-Hint
+Hint
135K
μ0H0 (T)
H0
+Hint
As -Hint
H∥c = H0 ± Hint
As
Hint
T(K)
∴As site： Hint ～1.5T
H∥ab ≒ H0
Antiferromagnetic order in FeAs layer
As
H II c
T≦135K
T≧135K
H II c
Hint
Fe
Fe
Fe
H0
Fe
As
Fe
BaFe2As2
H II c
This is consistent with Stripe AFM structure
by neutron diffraction experiment
Summary

Superconductivity appears in Fe - based system, when
carrier is doped and/or pressure is applied.
140
BaFe2As2
120
Ba1−xKxFe2As2
Tc [K]
100
80
AFM
60
40
20
SC?
0
1
2
3
4
5
6
Pressure [GPa]

In BaFe2As2, the magnetic structure evidenced by 75As NMR is consistent with stripe type AFM structure.
As
Fe

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