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Probing The Spin Pairing in The Superconducting State of (TMTSF) 2 ClO 4

Probing The Spin Pairing in The Superconducting State of (TMTSF) 2 ClO 4. UCLA J. Shinagawa, F. Zhang, B. Alavi and S.E. Brown Tokyo University (Kanoda’s group) Y. Kurosaki Harvey Mudd college C. Parker. Experimental Evidences Showing Higher Angular Momentum SC State.

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Probing The Spin Pairing in The Superconducting State of (TMTSF) 2 ClO 4

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  1. Probing The Spin Pairing in The Superconducting State of (TMTSF) 2ClO4 UCLA J. Shinagawa, F. Zhang, B. Alavi and S.E. Brown Tokyo University (Kanoda’s group) Y. Kurosaki Harvey Mudd college C. Parker

  2. Experimental Evidences Showing Higher Angular Momentum SC State Effects of non-magnetic disorder Effects of radiation (TMTSF)2PF6 (TMTSF)2(ClO4)1-x(ReO4)x doped pure damaged “pristine” M.-Y. Choi, et al. PRB 25 (1982) N. Joo, et al. cond-mat 0401420 (2004) • Superconducting state very sensitive to defects introduced by irradiation (e.g., Bouffard, et al. (1982); Abrikosov (1983))

  3. Are There Nodes or Not? Field Cycled 1H T1 Thermal Conductivity (TMTSF)2ClO4 (TMTSF)2ClO4 Normal SC M. Takigawa, H. Yasuoka, G. Saito JPSJ 56 (1987) S. Belin and K. Behnia, PRL 79, 2125 (1997) Power Law dependence showing the anisotropic nature(nodes) of gap along the FS. Y. Hasegawa, H. Fukuyama, JPSJ (1987)) No significant electronic contribution for T<Tc/2. Evidence for nodeless gap

  4. Is It Singlet? • Hc2 observed to exceed the Pauli pair-breaking limit (~2T) by 4 times or more... • I.J.Lee PRB 42 R14669(2000) Hp Not singlet?? I.J. Lee et al.PRL78 3555(1997)

  5. Spin Part of Knight Shift is Sensitive to Pairing State Knight shift probes the spin susceptibility of conduction electron through hyperfine coupling: K=Ks+Korb... =acs +bcvv... Singlet(s-wave) Triplet Al AL Hamond, PRL (1967) Ishida, et al. nature (1998)

  6. Previous Knight Shift Measurement on PF6 0.1 1 temp(K) But, T1 shows weak temperature dependence in SC state. Peak? What are possible causes? (1)Time dependent macroscopic filed due to the motion of vortices. (2)Quasiparticle (as from vortex cores) (3) collective excitations of triplet SC. T.Rostunov et.al, Condmat0506548 No change in Knight shift was observed. I.J. Lee et al.PRL (2002)

  7. Why ClO4? (1)SC can be obtained without pressure. The sample can be in direct contact with the LHe3 and the heating effect of the pulse expected to be less. (2)Recent study of Hc2 on ClO4 shows larger Hc2 than Pauli limit. These are all good enough reasons for us to go for another shot! Hp J.I. Oh and M. Naughton.PRL92 067001(2004)

  8. c* a 55° b’ Experimental Setup Field alignment EM response measurement to check the field penetration into layers. Angle resolution: dQ<0.05degree

  9. Heat Issues on Knight Shift Measurement In pulsed-NMR measurement, 100W of instantaneous power is dumped into the system. Is the sample in SC state during the acquisition of spectrum? ECHO T?? Temperature calibration curve ~200us Following Lee, et al., PRL (2002)

  10. Knight Shift Values a c* pz orbital of Se atom dominates the Aax, plus a small Aiso (following Takigawa et al, JPSJ 55, 1233) F. Zhang, Y. Kurosaki, J. Shinagawa, B. Alavi, and S.E. Brown, PRB(2005)

  11. Sample Characterization T1 of ClO4 shows clearer transition into SC state than PF6

  12. 77Se Knight Shift • Δf <-3kHz seen at the lowest temperature • Broadening more significant than shift?

  13. Effect on Se Hyperfine or Macroscopic Field Proton is weakly coupled to electron spins and therefore is sensitive only to the macroscopic field change. No macroscopic field change. Any shift or broadening seen in 77Se is all from the hyperfine coupling

  14. Comparison with Models For the lowest temperature point (Δfmeasured~3kHz@T=0.7K), with precisely determined Knight shift value we can estimate the expected frequency shift for singlet case. Fulde-Maki: takes into account pair breaking due to finite applied field. Δfmeasured <<Δfsinglet

  15. How Much is the SC Part? In worst case scenario, we can estimate the ratio of the normal state to the SC state. What is SC fraction?

  16. How Much is Superconducting ? Normal state relaxation are consistent with a model of 2D spin fluctuations For the superconducting state, Superconducting fraction 70%

  17. Subtraction of Normal Part from Spectrum No change to within S/N, consistent with previous measurements

  18. Conclusion New data here (1) 77SeT1 shows no significant coherentce peak and rate drops rapidly at measuring field (2) To within experimental uncertainty, no change in spin part of Knight shift in superconducting state (3)We are conducting CW and other pulse measurements in lower field and in lower temperature in SC state. Also improving S/N.

  19. Spin fluctuations and enhancement of spin-lattice relaxation • Treat response c(q,w)phenomenologically: • Response peaked at Q<>0 (as for AF) • Overdamped • Result in mean field (Moriya; Millis, Monien, Pines):

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