スライド 1

Superconductivity in
iron-based layered oxypnictide compound
Kitaoka Laboratory
Hiroki Yamashita
H.Takahasi et al ; Nature 453 , 376 (2008)
Kamihara ,Y et al ; J.Am.Chem.Soc. 130 , 3296 (2008)
Contents
Introduction
・History of superconductivity
・Comparison between Fe-based system and
High-Tc cuprate
Experiment
Summary
cuprate：銅酸化物
History of Superconductivity
200
Transition temperature (K)
High-Tc cuprate
metal
Iron-based system
1911
163
Hg-Ba-Ca-Cu-O
150
（at a suitable pressure）
Hg-Ba-Ca-Cu-O
Superconductivity was
discovered
Tl-Ba-Ca-Cu-O
Bi-Sr-Ca-Cu-O
100
High-Tc cuprate was
discovered
Y-Ba-Cu-O
77 nitrogen temperature
SmO0.9F0.11FeAs
50
La-Ba-Cu-O
Pb
Hg
0
1900
Nb
NbC
1920
1940
NbN
MgB
2
NbGe
1960
Year
1980
1986
LaO0.89F0.11FeAs
LaOFeP
2000
2020
2006
Iron-based system was
discovered
Comparison (1) Doping mechanism
High-Tc cuprate
iron-based system
charge reservoir layer
La
Cu
O
eSr2+
F
Electron dope (O2- → F-)
Hole dope (La3+ → Sr2+)
・ Layered structure (charge reservoir layer & conduction layer)
Comparison (2) Phase diagram
AF?
High-TC cuprate
Temperature
Temperature
Fe-based system
PM
AF
SC
electron density
Hole density
・Superconductivity appears by doping carriers.
・ Superconducting transition related to a magnetic instability.
Experiment
Electrical resistivity under various conditions
1.Carrier doping
2.Pressure
3.Substitution of La site
Search for highest TC in Fe-As compounds
Resistivity in LaO1-xFxFeAs
(x is amount of dope)
x
26K
?
・ Superconducting transition doesn’t occur by undoped sample.
・When x is 0.11,Tc is the maximam.
Enhancement of Tc by Pressure in LaO0.89F0.11FeAs
optimally doped
43
TC increase below 3GPa ,
but TC decrease above 3GPa .
Effect of substitution at La-site
atomic radius decrease
70
60
Maximum of Tc
Tc [K]
50
Nd
Pr
40
Ce
30
La
20
10
0
La Ce Pr Nd Pm Sm Eu Gd Td Dy
Atomic radius decrease
Sm
Gd
Suppression of Tc by Pressure in NdFeAsO0.6
As increasing pressure , TC decrease
Summary



New material base for high-TC
superconductivity was discovered
in Fe-As compound.
Superconductivity realizes by
doping the carrier.
TC can be tuned by applying
pressure or substitution at La-site.

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