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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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2 Content Introduction Heavy Fermion & Fermi Liquid Symmetry of SC state Inversion symmetry Experimental Data in CePt 3 Si Summary
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3 Heavy Fermion & Fermi Liquid conduction electron 4f-electrons localize at atom. Magnetic orderFermi liquid state by heavy electrons Kondo effect conduction electron rare earth ion RKKY interaction 4f-electrons are itinerant. Introduction
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4 Phase diagram of heavy fermion systems Unconventional SC around QCP mediated by magnetic fluctuations. Temperature (K) 0 Pressure QCP Magnetic order Non Fermi liquid Fermi Liquid Introduction
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5 Pair function orbital spin Spin partOrbital part Singlet (S=0) antisymmetricsymmetric (s,d..) Triplet (S=1) symmetricantisymmetric (p,f..) Introduction BCS-SCHigh-T C cuprate Ce based HF-SC UPt 3,Sr 2 RuO 4
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6 Centrosymmetric vs Noncentrosymmetric H-F SC Pt(1) Pt(2) CePt 3 Si CeRhSi 3 CentrosymmetricNoncentrosymmetric Cooper pair materials(ex)CeCu 2 Si 2 CePt 3 Si, UIr, CeRhSi 3 CeCu 2 Si 2 Si Cu Ce Introduction ±
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7 Noncentrosymmetric CePt 3 Si the first heavy fermion SC without a center of symmetry 1)SC ; cooper pairs formed by heavy quasiparticles (T C =0.75K) 2)AFM ; coexistence with SC on a microscopic scale (T N =2.2K) 3)High H c2 (0) 4)Anomalous behavior in 1/T 1 of NMR Pt(1) Pt(2) Novel SC state caused by lack of inversion symmetry ? key experimental features
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8 Resistivity & susceptibility T N =2.2K T C =0.75 K T.Yasuda et al., J.Phys Soc.Jpn.73, 1657 (2004) Coexistence of SC & AFM
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9 Specific heat Cp T C =0.75 K T N =2.2K C p /T=γ=390 [mJ/molK 2 ] ∝ 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+AT 2 Coexistence of SC & AFM
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10 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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11 H(T)-T(K) phase diagram H c2 (0) 5T > > H p 1T H p =1.84 * T C H P : Pauli-Clogston limiting field H=0H≠0H≠0 Spin-Singlet H=H P High Hc2(0) SC P-C Limit
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12 195 Pt nuclear spin-relaxation rate 1/T 1 LaPt 3 Si (La-NQR) s-wave CePt 3 Si (~1T) BW (full gap) p-wave LaPt 3 Si ; BCS s-wave model is applicable. CePt 3 Si ; Small jump at T c. However, overall T dependence is different from p-wave & BCS s-wave. Unusual T dependence of 1/T 1 T ⇒ s+p-wave pairing SC ?
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13 Noncentrosymmetric heavy fermion Ce-compounds T (K) 0 Pressure AFM SC CePt 3 Si CeRhSi 3 Pt(1) Pt(2) CePt 3 Si CeRhSi 3 : Pressured-induced SC
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14 Noncentrosymmetric heavy fermion Ce-compounds CePt 3 SiCeIrSi 3 CeRhSi 3 T N (K) (P=0) 2.25.01.6 T C (K)0.751.6 (2.5GPa) 0.85 (1.62GPa) H C2 (T)511.1 (2.5GPa) 7 (1.62GPa) γ(mJ/molK 2 ) (P=0) 390120 Novel SC states caused by lack of inversion symmetry & high H C2 (0) !? High Hc2(0) Fe 26 Co 27 Ni 28 Ru 44 Rh 45 Pd 46 Os 76 Ir 77 Pt 78
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15 Summary The SC exists even in the AFM state in CePt 3 Si. Novel cooper pairing state with the two-component order parameter composed of spin-singlet and spin-triplet pairing components may be realized in CePt 3 Si. Noncentrosymmetric heavy fermion Ce-compounds may be thought of as unconventional SC from the aspect of high H C2 (0).
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