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SPIN EXCITATIONS IN La 2 CuO 4 : CONSISTENT DESCRIPTION BY INCLUSION OF RING EXCHANGE

SPIN EXCITATIONS IN La 2 CuO 4 : CONSISTENT DESCRIPTION BY INCLUSION OF RING EXCHANGE. A.A.Katanin a,b and A.P.Kampf a a Instit u t f ü r Physik, Universit ä t Augsburg, Augsburg, Germany b Institute of Metal Physics, Ekaterinburg, Russia. Magnetic structure of La 2 CuO 4.

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SPIN EXCITATIONS IN La 2 CuO 4 : CONSISTENT DESCRIPTION BY INCLUSION OF RING EXCHANGE

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  1. SPIN EXCITATIONS IN La2CuO4 : CONSISTENT DESCRIPTION BY INCLUSION OF RING EXCHANGE A.A.Katanina,b and A.P.Kampfa aInstitut für Physik, Universität Augsburg, Augsburg, Germany bInstitute of Metal Physics, Ekaterinburg, Russia

  2. Magnetic structure of La2CuO4 Heisenberg model j i Ring-exchange term l k j i • Appears in next-to-leading order in t/U expansion of Hubbard model • First introduced in connection with 3He(see, e.g., M.Roger et al, Rev.Mod.Phys 55 1 (1983))

  3. La2CuO4 Experimental spin-wave dispersion at T=10K (R.Coldea et al, Phys. Rev. Lett. 86, 5377 (2001))

  4. The Heisenberg model with ring exchange • Previously estimated values of parameters [1]: • J=146 meV; J´=J´´=0.02J; J<10-3J, J[]/J=0.41 • The derivation of effective spin model from three-band Hubbard model [2] led to estimate J[]/J=0.11 • [1] R.Coldea et al, Phys. Rev. Lett. 86, 5377 (2001) • [2] E. Müller-Hartmann and A. Reischl,cond-mat/0105392.

  5. Calculational steps • The Dyson-Maleev representation for spin operators • Calculation of renormalized spin-wave spectrum The factors {} are the renormalization factors • Solution of the self-consistent equations

  6. La2CuO4

  7. The results of fitting of experimental data • Parameters of the modelJ = 151.9 meV, J = J = 0.025J, J[] = 0.24J • Groud-state magnetization • Spin stiffness and the perpendicular susceptibilitys = 23.8 meV, c = 206meV,  = 4.8·10-5 K-1 • Earlier estimate from fitting the spin-spin correlation length (T) at T>TN is s = 23.9 meV • Renormalization factorsZc = 0.96, Z = 0.63, Z = 0.68 • Interlayer coupling J /J = 1.0·10-3 • The Neel temperature TN = 328 K  TNexp = 325 K

  8. Conclusions • The exchange parameters of La2CuO4 are determined with account of quantum fluctuations from the best fit to magnon spectrum • The values of exchange parameters are in goodagreement with other experimental data on La2CuO4.

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