Orbital-Peierls State in NaTiSi2O6

TL;DR

This paper demonstrates that NaTiSi2O6 exhibits an orbital-Peierls transition driven by quantum fluctuations, with groundstate properties analyzed through multiple computational methods, confirming the experimental observation of simultaneous spin and orbital ordering.

Contribution

It provides a comprehensive computational analysis confirming the orbital-Peierls state in NaTiSi2O6, highlighting the role of quantum fluctuations and small crystal field effects.

Findings

Orbital-Peierls transition occurs in NaTiSi2O6.

Quantum fluctuations drive the transition.

Simultaneous spin and orbital ordering at the same temperature.

Abstract

Does the quasi one-dimensional titanium pyroxene NaTiSi2O6 exhibit the novel {\it orbital-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 quantum fluctuations in the spin-orbital sector drive the transition, explaining why canonical bandstructure methods fail to find it. The conclusion that NaTiSi2O6 shows an orbital-Peierls transition is therefore inevitable.