bonca LAW3M-05 Janez Bonča Physics Department, FMF, University of Ljubljana, J. Stefan Institute, Ljubljana, SLOVENIA Thermodynamic Properties.

www-f1.ijs.si/~bonca LAW3M-05

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


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


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


SrCu2(BO3)2


SrCu2(BO3)2


Space group of the CuBO3 plane:

Point group:

Including time-reversal

at H=0:

H>0:


Shastry-Sutherland model:

Shastry & Sutherland

Physica 108B (1981) 1069


Complete model:

Ts<395K


Symmetry of DM term 1

2

y

x

x

y

Inversion Symmetry:

Mirror Symmetry:


Computation:

Allowed tilted square lattices:


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).


Thermodyamic properties:

Entropy density:

Specific heat:

Uniform susceptibility:


Model parameters


Uniform Susceptibility

T(K)


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).


Energy spectrum

12

3

4


ESR spectrumH. Nojiri, et al.,J. Phys. Soc. Jpn. 72, 3243 (2003).


Spin Structure Factor S. El Shwaish, J. Bonca, C.D.Batista, and I. Sega, PRB 71,

014413 (2005)

Non-symmetry breaking D:


Symmetry breaking D:

T=0


Effect of Dx and Dy terms


B||c B||a

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


Neutron Scattering

Knetter, PRL92, 027204 (2004)


Neutron Scattering

Comparison ofFTLM with:

Kageyama et al. PRL, 845876 (2000).

S. El Shawish, J. Bonča, and I. Sega,

PRB 72,184409 (2005).


Neutron Scattering


B.D. Gaulin et al. PRL, 93267202 (2004).


PRB 72,184409 (2005).


Neutron Scattering



T=1.4K

FTLM results

Experiment


Neutron Scattering




PRB 72,184409 (2005).


Finite Doping Sr Cu2-xMx(BO3)2,

M=Zn,Mg

Leung & Cheng,PRB 69, 180403, (2005)

N=32, Nh=1

J’/J=0.62


Uniform susceptibility o

K.Kudo et al.cond-mat/0409178


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


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.

bonca LAW3M-05 Janez Bonča Physics Department, FMF, University of Ljubljana, J. Stefan Institute, Ljubljana, SLOVENIA Thermodynamic Properties.

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