1/14 Evidence for a Novel Pairing State in Noncentrosymmetric Superconductor CePt3Si: A 29Si-NMR Knight Shift Study Ref. • M. Yogi et al., J. Phys. Chem. Solids 67 (2006). • E. Bauer et al., Phys. Rev. Lett. 92, 027003 (2004). • T. Yasuda et al., J. Phys. Soc. Jpn. 73, 1657 (2004). Kitaoka Laboratory Nobukatsu Tamura Contents ・Introduction The lack of inversion symmetry The formation of Cooper-pairs ・Experimental Methods NMR measurement Knight shift ・Experimental Results ・Summary and Future work 2/14 The lack of inversion symmetry 3/14 Mirror Not match up !! Introduction ～ CePt3Si ～ 4/14 The crystal structure CePt3Si c Not match up ab CePt3Si has the crystal structure with lack of inversion symmetry. Introduction ～ the formation of Cooper-pairs ～ 5/14 Cooper-pair s-wave type Superconductivity is caused by the formation of Cooper-pairs. Introduction 6/14 Wave function of Cooper pair ψ(r1-r2;s1,s2) = Φ(r1-r2) F(s1,s2) orbital orbital part even function Φ (-(r1-r2)) =Φ (r1-r2) spin spin part spin-singlet F(s2,s1) = －F(s1,s2) s-wave d-wave odd function spin-triplet Φ (-(r1-r2)) = －Φ (r1-r2) F(s2,s1) = F(s1,s2) p-wave Introduction 7/14 Symmetric Cooper pair Non symmetric spin-singlet or spin-triplet mixture of spin-singlet and spin-triplet s-wave wave function d-wave mixture-state p-wave Cooper Pair has mixture state spin singlet + spin triplet Investigate that by NMR !! NMR~Nuclear Magnetic Resonance~ 8/14 I = 1/2 Hint H0 ＋ H = H0 + Hint － Knight shift ω+⊿ω =γH ω=γ H0 =γ (H0+Hint) K ⊿E = hγH0 = hω ±1/2 -1/2 Energy ω ω Zeeman splitting ⊿ω ω+⊿ω +1/2 ⊿E = hγ(H0 + Hint) = h (ω+⊿ω) K = ⊿ω / ω Knight shift 9/14 K = ⊿ω / ω K ω ω spin-singlet Al ⊿ω spin-triplet K = 0 (T<<TC) K decreases below Tc . K doesn’t decrease below Tc . Sr2RuO4 Magnetic order ( T < TN ) 10/14 TTN<< TTN Tc TN T < TN ⇒ Magnetic order T. Yasuda et al., J. Phys. Soc. Jpn. 73, 1657 (2004). 29Si-NMR spectrum 11/14 TN < T T = 4.2 K H0 = 2.0012T 0 T < TN 0 T = 0.142 K H0 = 2.0061T M. Yogi et al., J. Phys. Chem. Solids 67 (2006). 29Si-NMR spectrum (T < TN) 12/14 ω =γ H Si H = H0 + Hint 0 H0 powder 0 T = 0.142 K H0 = 2.0061T M. Yogi et al., J. Phys. Chem. Solids 67 (2006). 29Si-NMR spectrum Knight Shift T < Tc 13/14 (ω=γH0) Tc < T T < Tc M. Yogi et al., J. Phys. Chem. Solids 67 (2006). K doesn’t decrease below Tc . The Cooper pair of this SC is dominant spin-triplet. Summary 14/14 • CePt3Si is theoretically expected that the lack of inversion symmetry gives rise to a mixture of spin-singlet and spin-triplet Cooper pair. • Knight shift doesn’t decrease below Tc at 2T. • It suggests that the Cooper pair of CePt3Si is dominated by spintriplet component. Future work • Knight shift measurement is necessary under low magnetic fields. • Use single crystal sample without disorder.
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