会社名など e. bauer et al, phys. rev. lett. 92. 027003 (2004) m. yogi et al. phys. rev. lett....

15
会会会会会 E. Bauer et al, Phys. Rev. Lett. 92. 027003 (2004) M. Yogi et al. Phys. Rev. Lett. 93, 027003 (2004) Kitaoka Laboratory Takuya Fujii Unconventional superconductivity in Noncentrosymmetric Heavy- Fermion superconductors

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Page 1: 会社名など E. Bauer et al, Phys. Rev. Lett. 92. 027003 (2004) M. Yogi et al. Phys. Rev. Lett. 93, 027003 (2004) Kitaoka Laboratory Takuya Fujii Unconventional

会社名など

E. Bauer et al, Phys. Rev. Lett. 92. 027003 (2004)

M. Yogi et al. Phys. Rev. Lett. 93, 027003 (2004)

  Kitaoka   Laboratory  

Takuya Fujii

Unconventional superconductivity in Noncentrosymmetric Heavy-

Fermion superconductors

Page 2: 会社名など E. Bauer et al, Phys. Rev. Lett. 92. 027003 (2004) M. Yogi et al. Phys. Rev. Lett. 93, 027003 (2004) Kitaoka Laboratory Takuya Fujii Unconventional

2

Content

Introduction

Heavy Fermion & Fermi Liquid

Symmetry of SC state

Inversion symmetry

Experimental Data in CePt3Si

Summary

Page 3: 会社名など E. Bauer et al, Phys. Rev. Lett. 92. 027003 (2004) M. Yogi et al. Phys. Rev. Lett. 93, 027003 (2004) Kitaoka Laboratory Takuya Fujii Unconventional

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Heavy Fermion & Fermi Liquid

  conduction electron

4f-electrons localize at atom.

Magnetic order Fermi liquid state by heavy electrons

Kondo effect

conduction electron

rare earth ion

RKKY interaction

4f-electrons are itinerant.

Introduction

Page 4: 会社名など E. Bauer et al, Phys. Rev. Lett. 92. 027003 (2004) M. Yogi et al. Phys. Rev. Lett. 93, 027003 (2004) Kitaoka Laboratory Takuya Fujii Unconventional

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Phase diagram of heavy fermion systems

Unconventional SC around QCP mediated by magnetic fluctuations.

Tem

per

atu

re (

K)

0

Pressure

QCPMagnetic order

Non Fermi liquid

Fermi Liquid

Introduction

Page 5: 会社名など E. Bauer et al, Phys. Rev. Lett. 92. 027003 (2004) M. Yogi et al. Phys. Rev. Lett. 93, 027003 (2004) Kitaoka Laboratory Takuya Fujii Unconventional

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Pair function

)',( )()( ' ' ssχkΦcckF skskSS

orbital spin

Spin part Orbital part

Singlet

(S=0)

antisymmetric symmetric (s,d..)

Triplet

(S=1)

symmetric antisymmetric (p,f..)

)( )( kΦkΦ

)( )( kΦkΦ

Introduction

BCS-SC High-TC cuprateCe based HF-SC

UPt3,Sr2RuO4

Page 6: 会社名など E. Bauer et al, Phys. Rev. Lett. 92. 027003 (2004) M. Yogi et al. Phys. Rev. Lett. 93, 027003 (2004) Kitaoka Laboratory Takuya Fujii Unconventional

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Centrosymmetric vs Noncentrosymmetric H-F SC

Pt(1)

Pt(2)

CePt3SiCeRhSi3

Centrosymmetric Noncentrosymmetric

Cooper pair

materials (ex)CeCu2Si2 CePt3Si, UIr, CeRhSi3

CeCu2Si2

Si

Cu

Ce

Introduction

±

Page 7: 会社名など E. Bauer et al, Phys. Rev. Lett. 92. 027003 (2004) M. Yogi et al. Phys. Rev. Lett. 93, 027003 (2004) Kitaoka Laboratory Takuya Fujii Unconventional

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Noncentrosymmetric CePt3Si

the first heavy fermion SC without a center of symmetry

1) SC ; cooper pairs formed by heavy quasiparticles (TC=0.75K)

2) AFM ; coexistence with SC on a microscopic scale (TN=2.2K)

3) High Hc2(0)4) Anomalous behavior in 1/T1 of NMR

Pt(1)

Pt(2)

Novel SC state caused by lack of inversion symmetry ?

key experimental features

Page 8: 会社名など E. Bauer et al, Phys. Rev. Lett. 92. 027003 (2004) M. Yogi et al. Phys. Rev. Lett. 93, 027003 (2004) Kitaoka Laboratory Takuya Fujii Unconventional

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Resistivity & susceptibility

TN=2.2K

TC=0.75K

T.Yasuda et al., J.Phys Soc.Jpn.73, 1657 (2004)

Coexistence of SC & AFM

Page 9: 会社名など E. Bauer et al, Phys. Rev. Lett. 92. 027003 (2004) M. Yogi et al. Phys. Rev. Lett. 93, 027003 (2004) Kitaoka Laboratory Takuya Fujii Unconventional

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Specific heat Cp

TC=0.75K

TN=2.2K

Cp/T=γ=390 [mJ/molK2] m∝ *

λ-  like  anomaly at 2.2 K :

onset of long range magnetic order

jump around 0.75K:

the transition into a SC phase

C/T =γ+AT2

Coexistence of SC & AFM

Page 10: 会社名など E. Bauer et al, Phys. Rev. Lett. 92. 027003 (2004) M. Yogi et al. Phys. Rev. Lett. 93, 027003 (2004) Kitaoka Laboratory Takuya Fujii Unconventional

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Microscopic evidence of AFM & SC

N.Metoki ,J.Phys.: Cond. Mat 16 L207 (2004)

Ce

Coexistence of SC & AFM on a microscopic scale

Pt(2)

Page 11: 会社名など E. Bauer et al, Phys. Rev. Lett. 92. 027003 (2004) M. Yogi et al. Phys. Rev. Lett. 93, 027003 (2004) Kitaoka Laboratory Takuya Fujii Unconventional

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H(T)-T(K) phase diagram

Hc2(0) 5T > > Hp 1THp =1.84* TC

HP: Pauli-Clogston limiting field

H=0 H≠0

Spin-Singlet H=HP

High Hc2(0)

SC

P-C Limit

Page 12: 会社名など E. Bauer et al, Phys. Rev. Lett. 92. 027003 (2004) M. Yogi et al. Phys. Rev. Lett. 93, 027003 (2004) Kitaoka Laboratory Takuya Fujii Unconventional

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0.1

1

(1/T

1T )

/ (1/

T 1T)

TC

0.2 1T / TC

LaPt3Si (La-NQR)

BCS fitting2/kBTC = 3.6

CePt3Si ( ~ 1T)BW

2/kBTC = 4

line-node2/kB

195Pt nuclear spin-relaxation rate 1/T1

LaPt3Si (La-NQR)s-wave

CePt3Si (~1T)BW (full gap)

p-wave

LaPt3Si ;BCS s-wave model is applicable.

CePt3Si ;Small jump at Tc.However, overall T dependence is different from p-wave & BCS s-wave.

Unusual T dependence of 1/T1T ⇒ s+p-wave pairing SC ?

Page 13: 会社名など E. Bauer et al, Phys. Rev. Lett. 92. 027003 (2004) M. Yogi et al. Phys. Rev. Lett. 93, 027003 (2004) Kitaoka Laboratory Takuya Fujii Unconventional

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Noncentrosymmetric heavy fermion Ce-compounds

T (

K)

0

Pressure

AFM

SC

CePt3SiCeRhSi3

Pt(1)

Pt(2)

CePt3Si

CeRhSi3: Pressured-induced SC

Page 14: 会社名など E. Bauer et al, Phys. Rev. Lett. 92. 027003 (2004) M. Yogi et al. Phys. Rev. Lett. 93, 027003 (2004) Kitaoka Laboratory Takuya Fujii Unconventional

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Noncentrosymmetric heavy fermion Ce-compounds

CePt3Si CeIrSi3 CeRhSi3

TN(K)

(P=0)

2.2 5.0 1.6

TC(K) 0.75 1.6

(2.5GPa)

0.85

(1.62GPa)

HC2(T) 5 11.1

(2.5GPa)

7

(1.62GPa)

γ(mJ/molK2)

(P=0)

390 120 120

Novel SC states caused

by lack of inversion symmetry & high HC2(0) !?

High Hc2(0)

Fe26 Co27 Ni28

Ru44 Rh45 Pd46

Os76 Ir77 Pt78

Page 15: 会社名など E. Bauer et al, Phys. Rev. Lett. 92. 027003 (2004) M. Yogi et al. Phys. Rev. Lett. 93, 027003 (2004) Kitaoka Laboratory Takuya Fujii Unconventional

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Summary

The SC exists even in the AFM state in CePt3Si.

Novel cooper pairing state with the two-component order

parameter composed of spin-singlet and spin-triplet pairing

components may be realized in CePt3Si.

Noncentrosymmetric heavy fermion Ce-compounds may be

thought of as unconventional SC from the aspect of high

HC2(0).