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(Review Article). Kitaoka Lab. Mariko Nitta. Nature Physics Volume: 6, Pages: 645–658 Year published: (2010) 10.1038/NPHYS1759. Contents. Introduction - Discovery of Fe- pnictide superconductivity - Four structures of Fe- pnictide superconductivity

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kitaoka lab mariko nitta
(Review Article)

Kitaoka Lab.

Mariko Nitta

Nature Physics Volume: 6, Pages: 645–658 Year published: (2010)

10.1038/NPHYS1759

slide2
Contents
  • Introduction

- Discovery of Fe-pnictide superconductivity

- Four structures of Fe-pnictide superconductivity

- Common and different features between Fe-pnictide and cuprate

- Phase diagram of Fe-pnictide superconductivity

- Superconducting energy gap and its symmetry

  • Experiments & Results

- Jump in electronic specific heat at SC transition

- Thermal conductivity

- Relaxation rate 1/T1

  • Summary
slide3
Introduction

Discovery of Fe-pnictide superconductivity in 2008

1111 system

Fe:ferro magnetic element

LaFeAsO1-y

Fe

As

O

La

Superconductivity

magnetism

Tcmax~28 K

slide4
Introduction

Four structures of Fe-pnictide superconductivity

all systems have FeAs layer

distance between FeAs layers

Block layer

111 system

122 system

11 system

1111 system

BaFe2As2

FeSe

LiFeAs

LaFeAsO1-y

slide5
Introduction

Common and different features between Fe-pnictide and cuprate

CuO2 layer

(1)2D layered structure

FeAslayer

(2)electron/hole doping causes superconductivity

εF

εF

parent compound

(3)non-doped state shows magnetism

Fe-pnictide ; metal

Cuprate ; Mott insulator

E

E

La2-xSrxCuO4

(LSCO)

k

k

electron doping

122 system

BaFe2As2

single band

multi band

slide6
Introduction

Fe-pnictide superconductivity

Ba1-xKxFe2As2

BaFe2-xCoxAs2

BaFe2As2-xPx

BaFe2As2

Tetragonal

Tetragonal

Tc(K)

Tc(K)

T0

AFM

AFM

Orthor

Orthor

SC

SC

apply pressure

doping level

Lattice shrinking &

electron/hole doping

Tetragonal

Orthorhombic

Superconductivity appears

slide7
Introduction

superconducting energy gap and its symmetry

εF

ele

hole

E

multi band

s+-wave

k

nodal s+-wave

d wave

Sign changing between hole band and electron band

バンド間で符号反転が起こる。

slide8
Experiment (1)

Jump in electronic specific heat at SC transition

Energy gap : large

→Jump in specific heat at SC transition temperature Tc

slide9
Results (1)

Jump in electronic specific heat at SC transition

K-doped Ba122

gap size : large

Tc increases with gap size

⊿C/Tc(mJ mol-1K-2)

Co-doped Ba122

gap size : small

Tc(K)

BCS type SC

slide10
Experiment (2)

Thermal conductivity

conduction electron

HEAT

COOL

HOT

Carrier : electron and phonon

Conduction electron is responsible for the thermal conductivity

electron state at Fermi level

Thermal conductivity measurement at 0K

slide11
Experiment (2)

nodal gap

NS(E)

N0

EF

EF +Δ0

Thermal conductivity ~Doppler shift~

Full gap

NS(E)

full gap

N0

EF

EF +Δ0

nodal gap

slide12
Results (2)

Thermal conductivity

KFe2As2

Ni-doped

Co-doped

P-doped

10%

Co-doped

Thermal conductivity (normalized)

Thermal conductivity (normalized)

residual DOS atεF

particular for nodal gap

K-doped

4.8%

Co-doped

Magnetic field (H/Hc2)

Magnetic field (H/Hc2)

Full gap

nodal gap

slide13
Experiment (3)

Release the energy

  • Relaxation rate 1/T1 by NMR

What isT1??

T1 ~ spin-lattice relaxation time

I

e

nuclear spin

electronic spin

spin-lattice interaction

Energy-

transfer

Time constant T1

1/T1 measurement is a good probe for Fermi surface !

slide14
Results (3)
  • compare 1/T1in1111,122 K-doped,122 P-doped

“Ba122 K-doped”

“Ba122P-doped”

“La1111”

Ba

Ba

K

Fe

Fe

Fe

As

As

As

P

O

La

slide15
Results (3)

compare 1/T1in1111,122 K-doped,122 P-doped

“La1111”

“Ba122 K-doped”

“Ba122P-doped”

57Fe-

NMR

75As-NQR

~T5

~T3

nodal two gap

two-gapped type s wave

(unconventional SC)

slide16
Possible Scenario

Ba1-xKxFe2As2

LaFeAsO

BaFe2As2-xPx

(LaFePO)

As

P

Full gap

nodal two gap

Fe

Fe

As and P-height relate to gap symmetry???

slide17
Summary

mechanism of Fe-pnictide superconductors

εF

gap symmetry … full gap s+- type or

nodal gap s+-type

E

La1111

Tcmax~28K

Ba122 P-doped Tcmax~30K

k

Full gap

nodal two gap

electronic structure is described by multi-band picture

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