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Unconventional superconductivity in Noncentrosymmetric Heavy-Fermion superconductors

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

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Unconventional superconductivity in Noncentrosymmetric Heavy-Fermion superconductors

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  1. Unconventional superconductivity in Noncentrosymmetric Heavy-Fermionsuperconductors E. Bauer et al, Phys. Rev. Lett. 92. 027003 (2004) M. Yogi et al. Phys. Rev. Lett. 93, 027003 (2004) KitaokaLaboratory Takuya Fujii

  2. Content • Introduction • Heavy Fermion & Fermi Liquid • Symmetry of SC state • Inversion symmetry Experimental Data in CePt3Si Summary

  3. Introduction Heavy Fermion & Fermi Liquid RKKY interaction Kondo effect conduction electron conduction electron rare earth ion 4f-electrons are itinerant. 4f-electrons localize at atom. Magnetic order Fermi liquid state by heavy electrons

  4. Introduction Phase diagram of heavy fermion systems Non Fermi liquid Temperature (K) Magnetic order QCP Fermi Liquid 0 Pressure Unconventional SC aroundQCP mediated by magnetic fluctuations.

  5. UPt3,Sr2RuO4 BCS-SC High-TC cuprate Ce based HF-SC Introduction Pair function spin orbital

  6. CeCu2Si2 CeRhSi3 Introduction Centrosymmetric vs Noncentrosymmetric H-F SC ± Ce Cu Pt(2) Si Pt(1) CePt3Si

  7. key experimental features Noncentrosymmetric CePt3Si the first heavy fermion SC without a center of symmetry Pt(2) Pt(1) • SC ; cooper pairs formed by heavy quasiparticles (TC=0.75K) • AFM ; coexistence with SC on a microscopic scale (TN=2.2K) • High Hc2(0) • Anomalous behavior in 1/T1 of NMR Novel SC state caused by lack of inversion symmetry ?

  8. Resistivity & susceptibility TN=2.2K TC=0.75K Coexistence of SC & AFM T.Yasuda et al., J.Phys Soc.Jpn.73, 1657 (2004)

  9. Specific heat Cp C/T =γ+AT2 λ-likeanomaly at 2.2 K : onset of long range magnetic order TN=2.2K jump around 0.75K: the transition into a SC phase TC=0.75K Coexistence of SC & AFM Cp/T=γ=390 [mJ/molK2]∝m*

  10. Microscopic evidence of AFM & SC Ce Pt(2) Coexistence of SC & AFM on a microscopic scale N.Metoki ,J.Phys.: Cond. Mat16 L207 (2004)

  11. High Hc2(0) H(T)-T(K) phase diagram Hc2(0)  5T > > Hp 1T Hp =1.84＊TC HP: Pauli-Clogston limiting field H=0 H≠0 SC P-C Limit H=HP Spin-Singlet

  12. 195Pt nuclear spin-relaxation rate 1/T1 LaPt3Si ; BCS s-wave model is applicable. CePt3Si ; Small jump at Tc. However, overall T dependence is different from p-wave & BCS s-wave. LaPt3Si (La-NQR) s-wave CePt3Si (~1T) BW (full gap) p-wave Unusual T dependence of 1/T1T ⇒s+p-wave pairing SC ?

  13. Noncentrosymmetric heavy fermion Ce-compounds CeRhSi3 CePt3Si T (K) CeRhSi3: Pressured-induced SC AFM SC 0 Pt(2) Pressure Pt(1) CePt3Si

  14. High Hc2(0) Noncentrosymmetric heavy fermion Ce-compounds Novel SC states caused by lack of inversion symmetry & high HC2(0) !?

  15. 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).

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