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


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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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Spin excitations in la 2 cuo 4 consistent description by inclusion of ring exchange

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


Spin excitations in la 2 cuo 4 consistent description by inclusion of ring exchange

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))


Spin excitations in la 2 cuo 4 consistent description by inclusion of ring exchange

La2CuO4

Experimental spin-wave dispersion at T=10K

(R.Coldea et al, Phys. Rev. Lett. 86, 5377 (2001))


Spin excitations in la 2 cuo 4 consistent description by inclusion of ring exchange

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.


Spin excitations in la 2 cuo 4 consistent description by inclusion of ring exchange

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


Spin excitations in la 2 cuo 4 consistent description by inclusion of ring exchange

La2CuO4


Spin excitations in la 2 cuo 4 consistent description by inclusion of ring exchange

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


Spin excitations in la 2 cuo 4 consistent description by inclusion of ring exchange

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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