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Novel Phase Separation and Spin Dynamics of Lightly Doped La 2-x Sr x CuO 4 by La-NQR

Novel Phase Separation and Spin Dynamics of Lightly Doped La 2-x Sr x CuO 4 by La-NQR. Kitaoka Lab. Shimizu Sunao. Reference ) K. Ishida et al PhysRevLett.92.257001. Contents. Introduction. High-Tc cuprates La 2-x Sr x CuO 4 NQR measurement. Experimental data & results.

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Novel Phase Separation and Spin Dynamics of Lightly Doped La 2-x Sr x CuO 4 by La-NQR

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  1. Novel Phase Separation and Spin Dynamics of Lightly Doped La2-xSrxCuO4 by La-NQR Kitaoka Lab. Shimizu Sunao Reference ) K. Ishida et al PhysRevLett.92.257001

  2. Contents Introduction • High-Tc cuprates • La2-xSrxCuO4 • NQR measurement Experimental data & results Summary

  3. Cu O La or Sr Introduction : High-Tc cuprates block layer CuO2 layer block layer A.F. ; antiferromagnetism SC ; superconductivity

  4. Cu O La or Sr Introduction : La2-xSrxCuO4 1 La2CuO4 La : +3 O : -2 → Cu : +2 CuO2 plane La2-xSrxCuO4 La : +3 Sr : +2 O : -2 → Cu : +(2+x) crystal structure La2-xSrxCuO4

  5. Introduction : hole doping (into CuO2 plane) dX2-Y2 d3Z2-r2 Cu2+ ( Cu : 3d10 4s1) dxy , dyz , dzx CuO2 plane :electron in Cu’s 3d orbital :electron spin

  6. We studied the samples , X = 0.01 , 0.018 , and 0.024 , by NQR measurement. 0.024 0.01 0.018 Introduction : La2-xSrxCuO4 2 • X 　≦ 0.02 Below TN , AF order occurs • 0.02 ≦X AF(反強磁性） T (K) Spin glass phase appears at low temperature . SC（超伝導） SG（スピングラス） X Phase diagram La2-xSr2CuO4

  7. Introduction : La-NQR 1 ±7/2 La : I = 7/ 2 3νQ ±5/2 ±7/2 ±5/2 2νQ ±3/2 ±3/2 ±1/2 1νQ ±1/2 HQ HQ + Hint （電場勾配のハミルトニアン） （内部磁場を考慮したハミルトニアン）

  8. 3νQ 2νQ 1νQ Introduction : La-NQR 2 ① ③ ② ③ ② ☆ ① ☆ An example of NQR spectrum : X = 0.018

  9. Experiment : NQR spectra Non magnetic phase Magnetic phase (a) X=0.01 • Just bellow TN, • two types of signals (b) X=0.018 • Between TN and Tf , • two types of signals Phase separation NM and AFM (b) X=0.018 (a) X=0.01

  10. Experiment : Internal field • Above Tf , • Hint is different Nh(0.01) ≦ Nh(0.018) • As T goes to 0K , • Hint has a same value. Tf Hole localization ?

  11. Experiment : resistivity • Below TN , • the resistivity shows a metallic behavior • Below Tf , • the resistivity is semiconductive Hole localization Reference )

  12. Experiment : volume fraction X = 0.01 X=0.018 • X = 0.018 , magnetic order occurs gradually • X = 0.01 , rapidly orders to the extent of 90% NQR spectrum X = 0.01 Phase separation even in X = 0.01

  13. Experiment : X = 0.024 スペクトル Intensity × T(K) SC（超伝導） • No phase separation and so rapid order

  14. Experiment : X<0.02 vs 0.02<X • X < 0.02 As T goes from over TN to 0K , magnetic order occurs with phase separation Paramagnetic & Antiferromagnetic phase • X > 0.02 T (K) No phase separation AF AF(SG) • bellow TN Hole localization and spin freezing Holes can move and break AF order. • bellow Tf , Tg X Holes localize and spins freeze

  15. Summary • X < 0.02 , below TN , there is the phase separation of • non magnetism and antiferromagnetism. • Bellow Tg and Tf , holes localize and spins freeze . • Mobile holes break antiferro order.

  16. X = 0.024 ゴミ箱

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