会社名など e. bauer et al, phys. rev. lett. 92. 027003 (2004) m. yogi et al. phys. rev. lett....
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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
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Content
Introduction
Heavy Fermion & Fermi Liquid
Symmetry of SC state
Inversion symmetry
Experimental Data in CePt3Si
Summary
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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
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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
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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
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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
±
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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
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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
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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
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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)
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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
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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 ?
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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
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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
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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).