Europhys. Lett.
Volume 75, Number 6, September 2006
Page(s) 957 - 963
Section Condensed matter: electronic structure, electrical, magnetic, and optical properties
Published online 09 August 2006
Europhys. Lett., 75 (6), pp. 957-963 (2006)
DOI: 10.1209/epl/i2006-10197-2

Orbital-assisted Peierls state in $\chem{NaTiSi_2O_6}$

J. van Wezel1 and J. van den Brink1, 2

1  Institute-Lorentz for Theoretical Physics, Universiteit Leiden, P.O. Box 9506, 2300 RA Leiden, The Netherlands
2  Institute for Molecules and Materials, Radboud Universiteit Nijmegen, P.O. Box 9010, 6500 GL Nijmegen, The Netherlands

received 23 June 2006; accepted in final form 21 July 2006
published online 9 August 2006

Does the quasi-one-dimensional titanium pyroxene $\chem{NaTiSi_2O_6}$ exhibit the novel orbital-assisted Peierls state? We calculate its groundstate properties by three methods: Monte Carlo simulations, a spin-orbital decoupling scheme and a mapping onto a classical model. The results show univocally that for the spin and orbital ordering to occur at the same temperature -an experimental observation- the crystal field needs to be small and the orbitals are active. We also find that fluctuations in the spin-orbital sector drive the transition, explaining why bandstructure methods fail to find it. The conclusion that $\chem{NaTiSi_2O_6}$ shows an orbital assisted Peierls transition is therefore inevitable.

75.10.Pq - Spin chain models.
75.10.Dg - Crystal-field theory and spin Hamiltonians.
71.70.Ej - Spin-orbit coupling, Zeeman and Stark splitting, Jahn-Teller effect.

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