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Kitaoka lab. M1 Takayuki Nagai

Impurity Effect as a Probe for the Gap Function in the Filled Skutterudite Compound Superconductor PrOs 4 Sb 12 : Sb-NQR Study. Impurity Effect as a Probe for the Gap Function in the Filled Skutterudite Compound Superconductor PrOs 4 Sb 12 : Sb-NQR Study. Kitaoka lab. M1 Takayuki Nagai.

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Kitaoka lab. M1 Takayuki Nagai

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  1. Impurity Effect as a Probe for the Gap Function in the Filled Skutterudite Compound Superconductor PrOs4Sb12 : Sb-NQR Study Impurity Effect as a Probe for the Gap Function in the Filled Skutterudite Compound Superconductor PrOs4Sb12 : Sb-NQR Study Kitaoka lab. M1 Takayuki Nagai • Reference M.NISHIYAMA et al , JPSJ . 74 . 1938 (2005)

  2. Introduction - Cooper pairing in superconductors - 2 disparate SC states in PrOs4Sb12 & PrRu4Sb12 • Experiments - NQR experiment in Pr(Os1-xRux)4Sb12 • Discussion - impurity effect - symmetry of SC gap for PrOs4Sb12 • Summary Outline

  3. ξ anisotropic superconductor (strongly correlated electron systems) • pairing force via spin fluctuation d-wave point-node line-node Introduction : Cooper-pair in superconducting state s-wave superconductor (in many metals & alloys) • pairing force via lattice oscillation BCS theory does not apply to anisotropic superconductors.

  4. ～10K PrOs4Sb12 • No coherence peak just below Tc anisotropic superconductivity ～70K • low temperature 1/T1 doesn’t follow Tn-dependence ～T3 PrOs4Sb12 Introduction : PrOs4Sb12 & PrRu4Sb12 - Nuclear spin-lattice relaxation time T1 - PrRu4Sb12 • T-linear behavior in the normal state • coherence peak just below TC • exponential decrease below TC BCS (s-wave) superconductivity PrRu4Sb12 Ref : M.Yogi et al, Phys. Rev. B 67,180501(R) (2003)

  5. Cage of 12 pnictogen atoms Motivation : CEF state PrOs4Sb12 PrRu4Sb12 Γ4(magnetic) ⊿CEF~10[K] ⊿CEF~70[K] Γ1 ( non-magnetic) TC : 1.3 K TC : 1.85 K m* : 1.6m0 m* : 7.6m0 ΔC/TC: 110 ΔC/TC: 500 γ : 59 γ : 350 - 750

  6. Tunneling spectroscopy[2] Sb-NQR (1/T1)[1] anisotropic s-wave ? Isotropic gap ? Magnetic penetration depth[3,4] Thermal conductivity under H[5] ・Full gap ・@ low temperature point-node ? Anisotropic gap ? Motivation : Decision of gap structure of PrOs4Sb12 s-wave? anisotropic gap? new gap structure? [1] H. Kotegawa et al., PRL 90 027001 (2003) [2] H. Suderow et al., PRB 69 060504(R) (2004) [3] E. E. M. Chia et al., PRL 91 247003 (2003) [4] E. E. M. Chia et al., cond-matt/0411395 [5] K. Izawa et al., PRL 90 117001 (2003)

  7. PrRu4Sb12 PrOs4Sb12 Pr(Os1-xRux)4Sb12 Os 0.67Å Crossover between two different superconducting character Ru 0.65Å Motivation : TC in Pr(Os1-xRux)4Sb12 Ref : N.A. Frederick et al, Phys. Rev. B 71, 064508 (2005) Os is replaced with Ru

  8. Experiments : Sb-NQR spectrum of Pr(Os1-xRux)4Sb12 Hamiltonian PrOs4Sb12 Ru:10% 123Sb Ru:20% 3ν Q 3ν Q 2ν 2ν Q Q PrRu4Sb12 1ν 1ν Q Q PrOs4Sb12 PrRu4Sb12

  9. Above T～100K 1/T1 can be fitted excellently by theoretical rate equation. Short component Long component Experiments : Nuclear magnetization recovery curve • Below T～100K 1/T1 : 2 components Ru-neighborhood Os-neighborhood

  10. Below ～ 1K T1T∝ const. 1/T1 : finite Experiments : 1/T1 (short component) TC=1.85K TC=1.6K TC=1.4K Ru:20% PrOs4Sb12 Ru:10%

  11. Discussion @ low temperature From the present results NS(E) : finite in the Ru-doped samples increases with increasing x

  12. Ce(Ru1-xAlx)2 x=0.01 x=0 x=0.03 Ref : H. Mukuda et al. JPSJ No.67, No.6, pp.2101-2106 (1998) Discussion : Impurity effect -Residual DOS (s-wave) scattering by impurities Cooper pairs are not broken.

  13. TC=0.7K Impurity mixed Sr2RuO4 Line-node TC=1.48K N0 Point-node Pure Sr2RuO4 N0 εF εF+Δ Nres Nodes in the gap function Impurities induce the residual DOS Ref : K. Ishida. et al. Phys. Rev. B 56 (1996) Discussion : Impurity effect -Residual DOS (p-wave , d-wave) d-wave p-wave Line-node Point-node

  14. Experiments : 1/T1 (short component) TC=1.85K TC=1.6K TC=1.4K Below ～ 1K T1T∝ const. Ru:20% RDOS Gap has nodes PrOs4Sb12 Ru:10%

  15. due to the excitation toΓ4 Γ4 Γ1 Discussion Discussion due to c-f coupling

  16. ΔCEF TC β Discussion

  17. Strong evidence for the existence of nodes in the gap function • The increase in ΔCEF is responsible for the decrease in TC . isotropic gap RDOS PrRu4Sb12(s-wave) PrOs4Sb12 Pr(Os1-xRux)4Sb12 node in gap function Summary • Finite DOS at the Fermi level increases as Os atoms are replaced by Ru atoms.

  18. Discussion : Calculated results for the anisotropic gaps Ref : S.Schmitt-Rink , K.Miyake et al.PRL. 57(1986) 2575

  19. melt point (K) 3793 Pr 3306 Os Ru 2607 Sb 903.78 Introduction : Sb-flux method electric furnace Pr , Os , Ru as solute Sb as flux Pt melting pot High temperature cool down slowly Electric furnace:電気炉 Melting pot:るつぼ Sample separates out

  20. 1/T1 measurement ～0.8MHz 123Sb 121Sb FWHM～0.5MHz 49.9MHz FWHM:半値幅

  21. Experiments : Temperature dependence of 1/T1 (Long component) Above TC X=0.1, 0.2 : PrRu4Sb12 - like behavior

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