Kitaoka Laboratory Machiko Abe

1. Coexistence of Magnetism and Superconductivity in under-doped LSCO, high-Tc cuprates：μSR experiments Reference) “Coexistence of Static Magnetism with a Modulated Stripe Structure and Superconductivity by μSR Measurements in Underdoped La2-xSrxCuO4 (x=0.07)” K.Ishida et al.,unpublished (2005) Kitaoka Laboratory Machiko Abe

2. Contents • Introduction • Experiments • Summary Property of magnetism and superconductivity in LSCO（LaSrCuO）, high-Tc cuprates Susceptibility measurement Principle of μSR (muon spin relaxation) Experimental results of μSR

3. high-Tc cuprates HgCaBaCuO （high pressure） 160 HgCaBaCuO （high pressure） 140 TlCaBaCuO multilayered cuprates (my previous talk) HgCaBaCuO 120 TlCaBaCuO BiCaSrCuO 100 YBaCuO 80 Today’s talk 60 LaSrCuO 40 Nb3Ge V3Si LaBaCuO 20 NbN NbC Pb Nb-Al-Ge Nb3Sn Nb Hg 0 1910 1930 1950 1970 1990 High Temperature superconductors Superconducting history Tc(K) High-Tc cuprates have CuO2 plane year

4. La2-xSrxCuO4(LSCO) CuO2 plane O CuO2 plane Cu La3+ Sr2+ La-O layer Sr CuO2 plane La-O layer CuO2 plane hole doping into CuO2 plane La2-xSrxCuO4 La2CuO4 Antiferromagnetic insulator

5. ? magnetism in SC state!! Phase diagram La2-xSrxCuO4 AF : antiferromagnetism SG : spin glass (static magnetism) SC : superconductivity

6. ? x=0.07 (7%-doped LSCO) Motivation In under-doped La2-xSrxCuO4 static magnetism in SC state To obtain microscopic information, this μSR experiment was performed. (Muon Spin Relaxation)

7. 17K Susceptibility measurement : bulk information La2-xSrxCuO4 (x=0.07) superconducting diamagnetic shielding effect in normal state in SC state Tc=17K

8. μ+ π±μ± + νμ μ± e± + νe +νμ What’s muon(μ±) ? pion(π±) neutorinos neutorino proton Carbon atom nucleus muon(μ±) electron(e±) • polarized moving direction • gyromagnetic ratio γμ≒2π×13.5kHz/Gauss • unstable elemental particle (average life time : 2.2μs) • decay into an electron and neutorinos External field (偏極する) (磁気回転比) μ （素粒子） spin precession (歳差運動)

9. e+ ×106 times counter muon beam count the number of electrons μ+ count time relaxation function TF-μSR (Transverse Field Muon Spin Relaxation) observation of “internal field andfield distribution” （内部磁場） （磁場の分布） External field H0 counter sample ① Spin precesses around the local field ② Spin polarization decreases due to the internal field distribution local field(Hloc) = external field(H0) + internal field (Hint)

10. decreasing of polarization spin precession • λ： relaxation rate Hint： internal field internal field field distribution Fast Fourier Transformation FFT spectrum • linewidth of spectrum • K (Knight shift) Intensity (local susceptibility) H0 +Hint Field H0 （局所的な） Parameters obtained from TF-μSR relaxation function Hloc =H0 + Hint G(t) = A exp[-(λt)γ]cos(γμHloct + φ)

11. 17K 4K superconducting diamagnetic shielding effect TF-μSRat H0=1kOe Knight Shift →local susceptibility static internal field occurs below 4K in superconducting state?

12. 4K <at lowest temperature> Linewidth ：0～150 Oe ordered moments are distributed 0～0.17μB 4K Hμ～860 Oe /μB TF-μSR at H0=1kOe FFT spectra (H0=1kOe) relaxation rate nonmagnetic fraction internal field distribution becomes large below 4K

13. relaxation rate Magnetic excitation in normal state TF-μSRat H0=60kOe FFT spectra (H0=60kOe) magnetic correlation develops below 100K

14. Static magnetism SC Static magnetism SC Possible spin modulation Catenary-type modulations repraduce well the experimental data the small moment region →superconductivity ? <at low temperature>

15. Summary La2-xSrxCuO4 (x=0.07) Microscopic information obtained from TF-μSR is that・・・ • Static and distributed magnetism is confirmed below 4K (in SC state) • Superconductivity and magnetism coexist on the catenary-type stripe structure

17. Appendix ⅠStopping site of the implanted muon μ+ has a positive charge →attracted by negative ions La3+, Sr2+, Cu2+, O2-

18. Appendix Ⅱ