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Thermodynamic Properties of the Shastry Sutherland Model

Thermodynamic Properties of the Shastry Sutherland Model. Janez Bonča Physics Department, FMF, University of Ljubljana, J. Stefan Institute, Ljubljana, SLOVENIA. Collaborators: S. El Shawish and I. Sega , J. Stefan Inst., Ljubljana, Slovenia

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Thermodynamic Properties of the Shastry Sutherland Model

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  1. Thermodynamic Properties of the Shastry Sutherland Model Janez Bonča Physics Department, FMF, University of Ljubljana, J. Stefan Institute, Ljubljana, SLOVENIA

  2. Collaborators: • S. El Shawish and I. Sega, J. Stefan Inst., Ljubljana, Slovenia • C. D. Batista, M. Jaime, N. Harrison, G.A. Jorge, LANL T-11, NHMFL, USA • R. Stern, NICPB, Tallin, Estonia • H.A. Dabkowska, B.D. Gaulin, Mc Master Univ., Hamilton, Canada

  3. Introduction • Structure and symmetry properties of SrCu2(BO3)2 • The Sutherlad Shastry model • Finite Temperature Lanczos method • Specific heath results and comparison with experiment • Spin structure factor at zero and finite temperatures and comparison with ESR and INS measurements • Finite doping with nonmagnetic impurities

  4. SrCu2(BO3)2

  5. SrCu2(BO3)2

  6. Space group of the CuBO3 plane: Point group: Including time-reversal at H=0: H>0:

  7. Shastry-Sutherland model: Shastry & Sutherland Physica 108B (1981) 1069

  8. Complete model: Ts<395K

  9. Symmetry of DM term sx y 1 InversionSymmetry: sy x 2 MirrorSymmetry:

  10. Computation: Allowed tilted square lattices:

  11. FTLM: High -T expansion Thermal average over the canonical ensemble Combination of high- temperature expansion and random sampling J. Jaklič and P. Prelovšek, Adv. Phys. 49, 1 (2000). J. Jaklič and P. Prelovšek, Phys. Rev. Lett. 77, 892 (1996). J. Bonča and P. Prelovšek, Phys. Rev. B 67, 085103 (2002).

  12. Thermodyamic properties: Entropy density: Specific heat: Uniform susceptibility:

  13. Model parameters

  14. Uniform Susceptibility T(K)

  15. Specific heat G.A.Jorge, R.Stern, M. Jaime, N. Harrison, J. Bonča, S. El Shawish, C.D Batista, H.A. Dabkowska, and B.D. Gaulin,PRB71, 092403, (2005).

  16. Energy spectrum 3 4 2 1

  17. ESR spectrum H. Nojiri, et al.,J. Phys. Soc. Jpn. 72, 3243 (2003).

  18. Spin Structure Factor S. El Shwaish, J. Bonca, C.D.Batista, and I. Sega, PRB 71, 014413 (2005) Non-symmetry breaking D:

  19. Symmetry breaking D: T=0

  20. Effect of Dx and Dy terms

  21. H. Nojiri, et al.,J. Phys. Soc. Jpn. 72, 3243 (2003). B||c B||a

  22. Neutron Scattering Knetter, PRL 92, 027204 (2004)

  23. Neutron Scattering S. El Shawish, J. Bonča, and I. Sega, PRB 72,184409 (2005). Comparison of FTLM with: Kageyama et al. PRL, 84 5876 (2000).

  24. Neutron Scattering Comparison of FTLM with: B.D. Gaulin et al. PRL, 93 267202 (2004). S. El Shawish, J. Bonča, and I. Sega, PRB 72,184409 (2005).

  25. Neutron Scattering FTLM results Comparison of FTLM with: B.D. Gaulin et al. PRL, 93 267202 (2004). Experiment T=1.4K

  26. Neutron Scattering S. El Shawish, J. Bonča, and I. Sega, PRB 72,184409 (2005). Comparison of FTLM with: B.D. Gaulin et al. PRL, 93 267202 (2004).

  27. Finite Doping Sr Cu2-xMx(BO3)2, M=Zn,Mg J’/J=0.62 N=32, Nh=1 Leung & Cheng,PRB 69, 180403, (2005)

  28. Uniform susceptibility co K.Kudo et al. cond-mat/0409178

  29. Spin Structure Factor Sr Cu2-xMx(BO3)2, X=2n

  30. Conclusions • FT simulations of Cv show good agreement with experimental data when symmetry breaking DM term is of the order of Dz~5K. G.A.Jorge, R.Stern, M. Jaime, N. Harrison, J. Bonča, S. El Shawish, C.D Batista, H.A. Dabkowska, and B.D. Gaulin,PRB71, 092403, (2005). • ESR spectra can be reproduced only with finite value of symmetry breaking Dz – open question (structural phase transition, phonons). S. El Shwaish, J. Bonca, C.D.Batista, and I. Sega, PRB 71, 014413 (2005). • Good agreement with neutron-scattering data. S. El Shawish, J. Bonča, and I. Sega, PRB 72,184409 (2005). • Results a finite doping show filling up of the spin gap.

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