a new type iron-based superconductor ~k 0.8 fe 2-y se 2 ~
DESCRIPTION
A new type Iron-based superconductor ~K 0.8 Fe 2-y Se 2 ~. Kitaoka lab Keisuke Yamamoto. D.A.Torchetti et al , PHYSICAL REVIEW B 83 , 104508 (2011 ) W.Bao et al , arXiv:1102.0830v1 Feb (2011). Contents. Introduction Iron-based superconductor History Structure Characteristics - PowerPoint PPT PresentationTRANSCRIPT
A new type Iron-based superconductor ~K0.8Fe2-ySe2~
Kitaoka lab
Keisuke Yamamoto
D.A.Torchetti et al , PHYSICAL REVIEW B 83 , 104508 (2011)W.Bao et al , arXiv:1102.0830v1 Feb (2011)
Contents
• Introduction– Iron-based superconductor
• History• Structure• Characteristics
• Experiment ~K0.8Fe2-ySe2~
– Comparison to previous sample– NMR measurement
• Summary
2
History of superconductivity
under high pressure
0
50
100
150
200
SmO0.9F0.11FeAs
LaO0.89
F0.11FeAs
LaOFeP
Hg-Ba-Ca-Cu-O（ ）
Hg-Ba-Ca-Cu-O
Tl-Ba-Ca-Cu-O
Bi-Sr-Ca-Cu-O
Y-Ba-Cu-O
MgB2
NbGe
NbNNbC
NbPb
high-Tc cuprate
metal
iron-based system
Tra
nsiti
on te
mpe
ratu
re (
K)
1900 1920 1940 1960 1980 2000 2020
Year
Hg
La-Ba-Cu-O
Discovery of superconducting phenomenon
1911
1986
High-Tc cuprate superconductor
2006
Iron-based high-Tc superconductor
77
163
1979 Heavy fermion
superconductor
CeCu2Si2
heavy fermion system
PuCoGa5
Introduction
3
Iron-based superconductor
LaFeAsO BaFe2As2LiFeAs FeSe
Fe
As
Se
1111 system 122 system 111 system 11 system
Tc max = 55K Tc max = 38K Tc max = 18K Tc max = 8K
Fe-Pnictide layer
Introduction
Pnictgen(15 族元素 )4
Iron-based superconductorIntroduction
Band structure
Fermi suface
Phase diagram
5
hole
electron
nestinghole
electron
Iron-based superconductor
FeSe
DyPr
Ce
La
Er Ba
NaLi
Nd
Regular tetrahedron(109.5°)
Anion height
α
Fe
Pnictgen
6
Introduction
K0.8Fe2-ySe2
Characteristics
• isostructural to BaFe2As2
• relatively high Tc of ~33K
• heavily electron-doped system
Introduction
Cs0.8
K0.8 K0.8
Cs0.8
FeSe
DyPr
Ce
La
Er Ba
NaLi
Nd
Regular tetrahedron(109.5°)
TC TN TS
1111 ~55K ~140K ~155K
122 ~38K ~135K ~140K
K0.8Fe2-ySe2 ~33K ~560K ~580K7
J.Guo et al , PHYSICAL REVIEW B 82, 180520R 2010
Fermi surfaceExperiment
Previous superconductor K0.8Fe2-ySe2
8
Qian et al , arXiv:1012.6017v1 Dec (2010)
Band structure
Fermi suface
Band structure
Fermi suface
hole
electron
nestinghole
electron
hole
electronAbsence of the hole band
Phase diagramExperiment
Previous superconductor
AFM:antiferromagnetic ( 反強磁性 )SDW:spin density wave ( スピン密度波 )
M.Fang et al , EPL, 94 (2011) 27009
9
TS ,TN 140K~160K≒TcMAX 50K≒
TS,TN ≒ 300K ~ 500KTcMAX 33K≒
Expect higher Tc
K0.8Fe2-ySe2
M~3.31μB
Ordered stateExperiment
Previous superconductor
• Stripe magnetic order• Orthorhombic （斜方晶）
• unusual antiferromagnetic structure• Tetragonal （正方晶）• Fe vacancy order
M~0.5μB 10
Fe
As
W.Bao et al , arXiv:1102.0830v1 Feb (2011)
K0.8Fe2-ySe2
Electron-dopeExperiment
D.A.Torchetti et al , PHYSICAL REVIEW B 83 , 104508 (2011)
E
DO
S
EF0
～ kBT （ large ）
High temperature
E
DO
S
EF0
～ kBT （ small ）
Low temperature
Similar to the electron-doped systems among Fe-based superconductors
K0.8Fe2-ySe2
DOS : density of states11
Lack the hole bands near the zone center
AFSF(antiferromagnetic spin fluctuation)
• 1/T1T is enhanced toward Tc in both FeSe and the optimally doped Ba(Fe0.92Co0.08)2As2
enhancement of the AFSF
KxFe2-ySe2
Ba122(OVD)
Experiment
D.A.Torchetti et al , PHYSICAL REVIEW B 83 , 104508 (2011)
Tc
• In K0.8Fe2Se2 , there is no enhancement similarly to overdoped , nonsuperconducting Ba(Fe0.86Co0.14)2As2
Tc(Tc~25K)
(Tc~0K)
(Tc~33K)(Tc~9K)
Tc
12
FeSeBa122(OPT)
nestinghole
electron
Electron dope
Summary
• Introduction about K0.8Fe2-ySe2
• What is the reason of relatively high Tc ?– The structure of Fe-pnictide layer ?– Nesting between electron-band and hole-
band ?– High TN and Ts ?
This sample gives us a new point of view about Iron-based superconductors
13