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Janez BončaJanez Bonča
Physics Department, FMF, University of Physics Department, FMF, University of Ljubljana, J. Stefan Institute, Ljubljana, Ljubljana, J. Stefan Institute, Ljubljana,
SLOVENIASLOVENIA
Thermodynamic Properties of the Shastry Sutherland Model
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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
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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
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SrCu2(BO3)2
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SrCu2(BO3)2
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Space group of the CuBO3 plane:
Point group:
Including time-reversal
at H=0:
H>0:
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Shastry-Sutherland model:
Shastry & Sutherland
Physica 108B (1981) 1069
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Complete model:
Ts<395K
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Symmetry of DM term 1
2
y
x
x
y
Inversion Symmetry:
Mirror Symmetry:
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Computation:
Allowed tilted square lattices:
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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).
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Thermodyamic properties:
Entropy density:
Specific heat:
Uniform susceptibility:
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Model parameters
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Uniform Susceptibility
T(K)
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Specific heatG.A.Jorge, R.Stern, M. Jaime, N. Harrison, J. Bonča, S. El Shawish, C.D Batista, H.A. Dabkowska, and B.D. Gaulin,PRB 71, 092403,
(2005).
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Energy spectrum
12
3
4
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ESR spectrumH. Nojiri, et al.,J. Phys. Soc. Jpn. 72, 3243 (2003).
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Spin Structure Factor S. El Shwaish, J. Bonca, C.D.Batista, and I. Sega, PRB 71,
014413 (2005)
Non-symmetry breaking D:
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Symmetry breaking D:
T=0
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Effect of Dx and Dy terms
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B||c B||a
H. Nojiri, et al.,J. Phys. Soc. Jpn. 72, 3243 (2003).
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Neutron Scattering
Knetter, PRL92, 027204 (2004)
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Neutron Scattering
Comparison ofFTLM with:
Kageyama et al. PRL, 845876 (2000).
S. El Shawish, J. Bonča, and I. Sega,
PRB 72,184409 (2005).
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Neutron Scattering
Comparison ofFTLM with:
B.D. Gaulin et al. PRL, 93267202 (2004).
S. El Shawish, J. Bonča, and I. Sega,
PRB 72,184409 (2005).
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Neutron Scattering
Comparison ofFTLM with:
B.D. Gaulin et al. PRL, 93267202 (2004).
T=1.4K
FTLM results
Experiment
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Neutron Scattering
Comparison ofFTLM with:
B.D. Gaulin et al. PRL, 93267202 (2004).
S. El Shawish, J. Bonča, and I. Sega,
PRB 72,184409 (2005).
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Finite Doping Sr Cu2-xMx(BO3)2,
M=Zn,Mg
Leung & Cheng,PRB 69, 180403, (2005)
N=32, Nh=1
J’/J=0.62
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Uniform susceptibility o
K.Kudo et al.cond-mat/0409178
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Spin Structure Factor Sr Cu2-xMx(BO3)2, X=2n
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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,PRB 71, 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.