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Kitaoka Lab Kaneda Takuya

Magnetic states of lightly hole-doped cuprates in the clean limit as seen via zero-field muon spin spectroscopy. F. Coneri, S. Sanna, K. Zheng, J. Lord, and R. De Renzi, Phy. Rev. B 81 , 104507 (2010). Kitaoka Lab Kaneda Takuya. Contents. Introduction High- T c cuprate superconductors

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Kitaoka Lab Kaneda Takuya

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  1. Magnetic states of lightly hole-doped cuprates in the clean limit as seen via zero-field muon spin spectroscopy F. Coneri, S. Sanna, K. Zheng, J. Lord, and R. De Renzi, Phy. Rev. B 81, 104507 (2010) Kitaoka Lab Kaneda Takuya

  2. Contents • Introduction High-Tccuprate superconductors • Measurement muon spin rotation (μSR) • Result Phase diagram of YBa2Cu3O6+y • Conclusion

  3. High-Tc Cuprate Superconductors HgCaBaCuO （under high pressure） 160 160 HgCaBaCuO （under high pressure） TlCaBaCuO HgCaBaCuO TlCaBaCuO BiCaSrCuO 100 Tc (K) 100 YBaCuO 80 liquid nitrogen 60 LaSrCuO Nb3Ge V3Si LaBaCuO NbN NbC Pb Nb-Al-Ge Nb3Sn Hg Nb 0 0 1910 1990 (year) 1911 1986 Introduction Cuprate Superconductor Increase of Transition Temperature(Tc)

  4. High-Tc Cuprate Superconductors Introduction La2CuO4 La3+2-xBa2+xCuO4 La3+→Ba2+ d(x2-y2) Cu(3d104s1) 3d(x2-y2) 3d(3z2-r2) charge reservoir 電荷供給層 Cu2+x Cu+2 3d(xy) (3d9) CuO2 layer CuO2面 La (Ba) 3d(yz, zx) charge reservoir 電荷供給層 Cu crystal structure of La-Ba-Cu-O O La(Ba) electric conductivity with hole doping Superconductivity emerges with optimal doping.

  5. High-Tc Cuprate Superconductors Introduction charge reservoir CuO2 layer AFM AFM SC SC In order to understand the ground state of cuprate superconductor, careful study about its underdoped region is required.

  6. sample YBa2Cu3O6+yfor various oxygen-content y various hole density h CuO-chain CuO2 plane T (K) CuO2 plane hole density

  7. Measurement What is μSR (muon spin rotation) ? Property of Muon • spin: I = ½ • gyromagnetic ratio: 135.53MHz/T • mean lifetime: 2.2μs It’s very sensitive even to low magnetic field. pion mean lifetime: 26ns

  8. Measurement What is μSR (muon spin rotation) ? H detected!! internal field • Internal field many muons sample Sμ muon (μ+) positron about t μs later… positron counter Internalfield is determined from time dependence of muon asymmetry. • The positron emission in the muon decay is asymmetric. • Eech muon has different life.

  9. μSR Result Result h=0.02 T (K) h=0.04 only depend on muon’s life hole density Internal field is not static. damped oscillation h=0.07 static field

  10. Temperature dependence of the moment Result Re-entrant m :magnetization h :hole density BAO :internal field at the apical oxygen TN Thermally activated T (K) • TN drop rapidly with increasing the hole density h. • For h =0.035, m(h,T) deviates from power-law behavior (dashed line) and an upturn (solid line) appears. hole density Thermally activated regime (high temperature) & Re-entrant regime (low temperature)

  11. Activation temperature TA Result hole doping extrapolation of the m(h,T) power-law TA hole dependence of TA

  12. Result Phase diagram AFM phase is separeted into two regimes. • Re-entrant regime • Holes are localized. • Spins are freezing. • The moment recovers to 0.6μB. • Thermally activated regime • Holes are delocalized. AFM Thermally activated SC Re-entrant AFM phase vanishes at SC phase emerges at QCP!!

  13. Holes in CuO2 layer… hole spin Holes are localized. Spins are freezing. Holes are delocalized.

  14. Conclusion Re-entrant and Thermally Activated • There are two distinct regimes in AFM phase. • In re-entrant regime holes are localized and spins are freezing. • The critical hole density hc and hs have the same value. And the value h = 0.056 is a quantum critical point (QCP) for the cuprate clean limit.

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