会社名など E. Bauer et al, Phys. Rev. Lett (2004) M. Yogi et al. Phys. Rev. Lett. 93, (2004) Kitaoka Laboratory Takuya Fujii Unconventional superconductivity in Noncentrosymmetric Heavy- Fermion superconductors

2 Content Introduction Heavy Fermion & Fermi Liquid Symmetry of SC state Inversion symmetry Experimental Data in CePt 3 Si Summary

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

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

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

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 ±

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

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

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

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)

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

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 ?

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

14 Noncentrosymmetric heavy fermion Ce-compounds CePt 3 SiCeIrSi 3 CeRhSi 3 T N (K) (P=0) T C (K) (2.5GPa) 0.85 (1.62GPa) H C2 (T)511.1 (2.5GPa) 7 (1.62GPa) γ(mJ/molK 2 ) (P=0) 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

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).