Transcript スライド 1

Fe
Superconductivity in
system AFe2(As1-xPx)2
As
A = Ca, Sr, Ba
Evolution from non-Fermi- to Fermi-liquid transport via
isovalent doping in BaFe2(As1−xPx)2 superconductors
Kasahara et. al., Phys. Rev. 81, 184519(2010)
Dulguun Tsendsuren
Kitaoka Lab.
Division of Frontier Materials Sc.
Department of Materials Engineering Sc.
Graduate School of Engineering Sc., Osaka Univ.
History of Superconductivity
Transition temperature (K)
200
metal
heavy fermion system
high-Tc cuprate
163
1911
Hg-Ba-Ca-Cu-O
iron-based system
150
Introduction
（under high pressure ）
Hg-Ba-Ca-Cu-O
Tl-Ba-Ca-Cu-O
Bi-Sr-Ca-Cu-O
100
Y-Ba-Cu-O
77
Discovery of
superconductivity
1979
Heavy fermion
superconductor
1986
50
MgB2
Pb
Hg
0
1900
Nb
NbC
1920
1940
La-Ba-Cu-O
PuCoGa5
NbGe
NbN CeCu2Si2
1960
Year
1980
2000
SmO 0.9F 0.11FeAs
High-Tc cuprate
superconductor
LaO 0.89F 0.11FeAs
LaOFeP
2020
2006
Iron-based high-Tc
superconductor
Iron-based Superconductors
42226
1111
122
Fe
Introduction
111
As
Today’s talk
Each system has FeAs layer
11
AFe2As2 System
Introduction
CaFe2As2
SrFe2As2
BaFe2As2
CaFe2(As1-xPx)2
SrFe2(As1-yPy)2
BaFe2(As1-zPz)2
iso-valent doping
Role of FeAs layer in 122 system
Full gap
Density of State
Density of State
Superconducting gap
gap
Introduction
Nodal gap
Energy
EFermi
gap
EFermi
Energy
Structure
Substance
Tc [K]
Structure
Substance
Tc [K]
42622
CaAlOFeAs
27
42622
SrScOFeP
17
1111
NdFeAsO
55
1111
LaFePO
5
122
Ba1-xKxFe2As2
38
122
BaFe2(As1-xPx)2
31
1.
2.
3.
4.
Spin-Lattice Relaxation Rate (by NMR)
Magnetic Penetration Depth
Thermal Conductivity
Specific Heat
Relaxation rate 1/T1 by NMR
Introduction
T1: spin-lattice relaxation time
Releases the energy
H0
Spin-Lattice interaction
nuclear
spin
H0
I
e
Energy Transfers in
almost T1 time
electronic
spin
How to verify SC gap?
Spin-Lattice Relaxation Rate
(by NMR)
1 1
[s ]
T1
T1 : Spin-Lattice relaxation time
Nodal gap:
Temperature
Linear
relation
Full gap:
Temperature
Non-Linear
relation
Introduction
Resistivity of BaFe2(As1-xPx)2
Exp. Result
Resistivity:
1. T0 Structure transition
2. TSDW AFM Order
3. Tcon Superconductivity appears
Resistivity reflects phase transition
clearly as other transport properties
Phase Diagram of BaFe2(As1-xPx)2
Exp. Result
Transitions:
Structure
SDW
onset Tc
Bulk Tc

Doping level (x) of P in BaFe2(As1-xPx)2
At x = 0.26
Tcmax = 31 [K]
Resistivity of BaFe2(As1-xPx)2
Exp. Result
Resistivity:   0  AT 
Fermi-liquid:   2.0 Tc = 0[K]
AFM fluctuation:   1.0 Tc = 31[K]
(Non-Fermi-liquid)
Highest Tc is clearly related
to AFM fluctuation
Fermi Surfaces vs. Doping
BaFe2As2
Ba0.8K0.2Fe2A2
hole doping
(K at Ba)
2D like FS
Full gap
Calculation
Tcmax = 38[K]
BaFe2P2
iso-valent
doping
(P at As)
Tcmax = 31[K]
3D like FS
Nodal gap
1. Full gap shows higher Tc compared with Nodal gap
2. With 3D like FSs, SC gap becomes Nodal gap
CaFe2(As1-xPx)2
Exp. Result
Fermi surfaces:
Tcmax = 15 [K], at x = 0.05
Tetragonal (SC)
c-Tetra. (NC)
1.
2.
3.
SC occurs in tetragonal structure
In c-Tetra., FS changed into 3D
SC disappears in c-Tetra
Summary
1. Superconductivity occurs:
1. AFM fluctuation appears nearby high Tc SC region
2. With structural change (Orthorhombic to Tetragonal)
2. Fermi Surface is structure dependent. In most cases, SC
occurs when FSs are like 2D
3. Essence of Full gap is one of promising key to increase Tc
in Superconductivity
Thank you
for your attention