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Antiferromagnetic Resonances and Lattice & Electronic Anisotropy Effects

Antiferromagnetic Resonances and Lattice & Electronic Anisotropy Effects in Detwinned La 2-x Sr x CuO 4 Crystals. Adrian Gozar #. G. Blumberg & B. Dennis. #. Crystals: Yoichi Ando & Seiki Komyia. CRIEPI, Japan. A. Gozar et al. Phys. Rev. Lett. ‘04.

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Antiferromagnetic Resonances and Lattice & Electronic Anisotropy Effects

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  1. Antiferromagnetic Resonances and Lattice & Electronic Anisotropy Effects in Detwinned La2-xSrxCuO4 Crystals Adrian Gozar # G. Blumberg & B. Dennis # Crystals: Yoichi Ando & Seiki Komyia CRIEPI, Japan A. Gozar et al. Phys. Rev. Lett. ‘04

  2. What is (detwinned) La2-xSrxCuO4 ? LTO R.J. Birgeneau PRL ‘87 b = 5.4 A b - a ~ 0.05 A a a b b Y.Horibe PRB ‘00 T(K) HTT adapted from B. Keimer et al. PRB 46, 14034 ‘92 500 HTT (tetragonal) 400 LTO (orthorhombic) 300 200 100 AF SC 0.02 0.1 0.2 x(Sr)

  3. Swapping the Crystal Axes with Magnetic Field room temperature H ~ 14 T c a(b) 1 mm a(b) H b b In a magnetic field H // CuO2 planes the b orthorhombic axis follows the direction of the external field  strong magneto-elastic coupling  net ferromagnetic moment ? La1.99Sr0.01CuO4 TN ~ 210K A.N. Lavrov Nature ‘02

  4. Outline  Long Range Antiferromagnetic Order in La2-xSrxCuO4  Magnetic Field Dependent Raman Data in La2-xSrxCuO4 x(Sr)  0.01  low energy magnetic excitations ► anisotropic dispersions of spin wave gaps ►in H  11 T  observation of magnetic field inducedspin ordering (H // b-axis)  Strong Lattice and Electronic Anisotropies ► detwinned La2-xSrxCuO4x(Sr)  0.03 ► CuO6 tilt disorder at x(Sr) = 1/8 doping in (La,Nd)2-1/8Sr1/8CuO4

  5. Spin Hamiltonian Excitations c 2D Heisenberg b a J ~ 140 meV ‘XY’ exchange anisotropy R. Coldea PRL ’01 Cu2+  / J ~ 10-4 (3/4,1/4) (0,0) (1/2,0) ‘DM’ Dzyaloshinskii-Moriya (k) CuO2 plane c XY ~ m(2J)1/2 J d / J ~ 7  10-3 DM ~ md  d b B. Keimer Z. Phys ’93 0 k Antiferromagnetic Order in La2-xSrxCuO4 (x  0.02) only in the LTO phase

  6. Spin-Wave Gaps in La2CuO4 T = 80 K 1 meV ~ 8 cm-1 (k) ~ 2 meV XY ~ m(2J)1/2 DM ~ md Raman Scattering 0 k La2CuO4 C.J. Peters PRB ’88 Neutron Scattering

  7. Spin-Wave Gaps in La2CuO4 T. Thio PRB ’90 CuO2 plane H c T = 80 K b (k) XY ~ m(2J)1/2 DM ~ md 0 k 1 meV ~ 8 cm-1 La2CuO4 C.J. Peters PRB ’88 Raman Scattering Neutron Scattering

  8. Spin-Wave Gaps in La2CuO4 CuO2 plane c XY DM DM = 17.0 cm-1 2D Spin-Wave Model b 1 meV ~ 8 cm-1 Raman Scattering Experiment

  9. Spin-Wave Gaps in La2CuO4 b 1 meV ~ 8 cm-1 Raman Scattering Experiment

  10. Magnetic Field Induced Raman Modes in La2CuO4 T (K) 300 200 100 0 H // b

  11. Field Induced Spin Reorientation (B) T = 300 K ► TN (La2CuO4) = 310 K & dTN / dHb ~ -1K/T CuO2 plane H = 0 c strong H // b b (A) T = 10 K ► Spin-Wave calculation is consistent (up to 5%) with the dispersion of the XY gap B. Keimer Z. Phys. ’93 ► XY ~ 5.5 meV (44 cm-1) ► For H // b  d DM / d Hb < 0 one expects a magnetic field induced transition c

  12. Field Induced Spin Reorientation is this a ‘regular’ spin-flop like transition ? (continuous) spin reorientation in the (bc) plane (A) T = 10 K ► Spin-Wave calculation is consistent (up to 5%) with the dispersion of the XY gap B. Keimer Z. Phys. ’93 ► XY ~ 5.5 meV (44 cm-1) ► For H // b  d DM / d Hb < 0 one expects a magnetic field induced transition (B) T = 300 K ► TN (La2CuO4) = 310 K & dTN / dHb ~ -1K/T c 300 K DM strong H // b d ≠ 0  = 0

  13. Field Induced Spin Reorientation T (K) 300 200 100 0 H // b 9 T

  14. Field Induced Spin Reorientation La1.99Sr0.01CuO4 La2CuO4 TN TN (La1.99Sr0.01CuO4) = 210 K dTN / dHb ~ -4 K / T

  15. Field Induced Spin Reorientation XY DM ► I(T) peaked at TN ► (T) > 0 at all temperatures La1.99Sr0.01CuO4 TN TN (La1.99Sr0.01CuO4) = 210 K dTN / dHb ~ -4 K / T

  16. Field Induced Spin Reorientation La1.99Sr0.01CuO4 H = 0 TN c net ferromagnetic moment b TN (La1.99Sr0.01CuO4) = 210 K dTN / dHb ~ -4 K / T

  17. Lattice & Electronic Anisotropy - La2-xSrxCuO4 2 1 La/Sr (aa) x = 0.01 (bb) (aa) x = 0.03 (bb) Raman shift (cm-1) c T = 10 K 1 2 (aa) x = 0 (bb) b a Raman response (rel. units)

  18. Local Structure at x ~ 1/8 Sr Doping 2 1 La/Sr ► no signatures of charge super modulation in (cc) polarized Raman spectra - group theory for the LTO phase predicts 5 fully symmetric Raman active modes ► at 1/8 Sr doping there exists substantial disorder in the CuO6 octahedra tilt pattern La2-x-yNdySrxCuO4 T = 10 K (cc) polarization 1 2 A. Gozar PRB ’03

  19. Conclusions  Magnetic Excitations ► DM and XY anisotropy induced spin-wave gaps ►For fields H // b  observation of magnetic field inducedspin reorientation  Low Energy Lattice & Electronic Dynamics ► detwinned La2-xSrxCuO4 x(Sr)  0.03 - about 30% anisotropy in the electronic background - strong phononic anisotropy ► x(Sr) = 1/8 (La,Nd)2-xSrxCuO4 - disorder in the local structure  lattice has to be taken into account when discussing possible spin or charge modulation in LaSrCuO

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