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Antiferromagnetic spin fluctuation and Superconductivity. Y. Nakai et al., PRB 87, 174507 (2013). Kitaoka Lab. M1 Y usuke Yanai. Contents. Introduction ・ History of Superconductivity ・ AFM and Superconductivity ・ Character of AFM spin fluctuation Analysis on spin fluctuations

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Antiferromagnetic spin fluctuation and superconductivity

Antiferromagnetic spin fluctuation and Superconductivity

Y. Nakai et al., PRB 87, 174507 (2013)

Kitaoka Lab. M1

Yusuke Yanai


Contents

  • Introduction

  • ・ History of Superconductivity

  • ・ AFM and Superconductivity

  • ・ Character of AFM spin fluctuation

  • Analysis on spin fluctuations

  • ・Ba(Fe1−xCox )2As2

  • ・BaFe2(As1−xPx )2

  • Result & Discussion

  • Summary


introduction

History of Superconductivity

1900

1920

1940

1960

1980

2000

2020

Year

metal superconductor

200

metal

heavy fermion system

electron-phonon interaction

high-Tccuprate

163

Hg-Ba-Ca-Cu-O

iron-based system

under high pressure

150

Heavy fermion superconductor

Hg-Ba-Ca-Cu-O

Tl-Ba-Ca-Cu-O

Bi-Sr-Ca-Cu-O

100

Transition temperature (K)

Y-Ba-Cu-O

77

High-Tccuprate superconductor

SmO

F

FeAs

50

0.9

0.11

MgB2

La-Ba-Cu-O

FeAs

LaO

F

PuCoGa5

Nb

Ge

0.11

0.89

Nb

Iron-based high-Tc superconductor

Pb

CeCu2Si2

NbN

LaOFeP

Hg

NbC

0


introduction

AFM and SC

Temperature

valence transition

HF

q = 0

ferromagnetism

valence/spin fluctuation

Tc~ 1K

AFM

SC

Pressure

TS

Temperature

Iron-based

TN

spin/orbital fluctuation

Tc~ 50K

q = Q (π , π)

antiferromagnetism

AFM

SC

Doping fraction

Cuprate

Temperature

spin fluctuation

Tc~ 100K

AFM

q : wave vector

SC

Doping fraction


introduction

  • Character of AFM spin fluctuation

  • Spin fluctuation parameter T0 and TA

χ’’(Q,ω)

q=Q (π , π)

χq

ω

Temperature

q = Q (π , π)

antiferromagnetism

AFM

SC

Doping fraction

q


introduction

  • Character of AFM spin fluctuation

  • Spin fluctuation parameter T0 and TA

χ’’(Q,ω)

∝TA

1/ξ

q=Q (π , π)

χq

ω

Temperature

q = Q (π , π)

antiferromagnetism

∝T0

AFM

SC

ΓQ

Doping fraction

q

ξ : magneticcorrelation length

ΓQ : characteristic energy


motivation

  • Relationship between T0and Tc , TA and TC

Cuprate

HF

HF

Cuprate

Tc∝ TA3/4T01/4

Higher T0 , TA

enhance pairing interaction

Iron-

based

Higher Tc


BaFe2As2

  • crystal structure of BaFe2As2

Co-dope

(electron-doping)

P-dope

(isovalent-doping)

  • Ba(Fe1-xCox)2As2

  • BaFe2(As1-xPx)2

F. L. Ning et al. ,

PRL 104, 037001(2010)

Y. Nakai et al.,

PRB 81, 020503R(2010)


Release the energy

Spin lattice relaxation time T1

(Dynamic information)

T1

1/T1T is generally expressed by

in SCR theory

Time constant T1

∝ χQ∝

Energy transfer

Electronic spin system

Nuclear spin system


  • Analysis on spin fluctuations in Ba(Fe1−xCox )2As2

( 1/T1T )obs.

loc.

( q independent )

1/T1T (sec-1K-1)

loc.

Temperature (K)

K = Kspin + Kchem(0.15%)

loc.

K (%)

Kspin

Kchem (0.15%)

Temperature (K)


For QCP(θ =0 ),

= const.

QCP

0.05 < x < 0.08


determine y0, T0, and TA

y0 : parameter characterizing

the closeness to QCP

1/T1T

y0

NMRexperiment

γ

T0

specific heat experiment

χ(Q,ω)

TA

neutron scattering experiment


1/T1

Electric resistivity (Ba(Fe0.92Co0.08)2As2)

SCR calculation

SCR calculation

experiment

experiment

very good agreementwith

the experimental data

SCR theory


  • Analyze BaFe2(As1-xPx)2

  • in the same way

For QCP,

= const.

QCP

x ~ 0.33


1/T1

Electric resistivity

~T 1

experiment

SCR calculation

experiment

SCR calculation

away from the QCP

crossover to a Fermi-liquid-like T 2

very good agreement

with the experimental data

SCR theory


  • QCP and Tc max

  • Ba(Fe1-xCox)2As2

  • BaFe2(As1-xPx)2

QCP

x ~ 0.33

QCP

x ~ 0.06

Tc max

x ~ 0.3

Tc max

x ~ 0.06

QCP ≃ Tc max


TcvsT0

χ’’(Q,ω)

0.06

(OPT)

Iron-based

HF

Cuprate

0.08

ω

SC & AFM

∝T0

HF

Iron-based

Cuprate

Tc~ 1K

Tc~ 50K

Tc~ 100K


  • TcvsTA

Cuprate

Iron-based

HF

χq

SC & AFM

∝TA

HF

Iron-based

Cuprate

Tc~ 1K

Tc~ 50K

Tc~ 100K

q

q=Q (π , π)


  • TN and TC

Result

TN

Cuprate

Iron-based

Cuprate

Iron-based

HF

HF

Temperature

AFM

PQ : antifferromagnetic moment per magnetic atom at T=0K

SC

Doping fraction


Summary

  • NMR and resistivity data of Ba(Fe1-xCox)2As2,

  • BaFe2(As1-xPx)2 are simulated by SCR theory.

  • The concentration of maximum Tc corresponds to

  • that of AF QCP.

AFM fluctuation plays an important role for SC.

  • Along with HF and cuprate, for iron-based

  • superconductors, higher T0 and TA give higher Tc.

  • The physics of iron-based may be closely related to the physics of HF and cuprate.


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