Spin-Peierls transition in TiOCl

TL;DR

This paper investigates the spin-Peierls transition in TiOCl, revealing a lattice symmetry lowering at 90 K and the formation of spin-singlet pairs below 66 K, establishing TiOCl as a pure 1D spin-Peierls system.

Contribution

It provides the first detailed experimental evidence that TiOCl is a pure 1D spin-Peierls system with negligible superexchange influence.

Findings

Phase transition at 90 K involves lattice symmetry lowering.

Below 66 K, a twofold superstructure indicates spin-singlet formation.

The transition at 66 K is first-order due to competition between phases.

Abstract

Temperature-dependent x-ray diffraction of the low-dimensional spin 1/2 quantum magnet TiOCl shows that the phase transition at T_{c2} = 90 K corresponds to a lowering of the lattice symmetry. Below T_{c1} = 66 K a twofold superstructure develops, that indicates the formation of spin-singlet pairs via direct exchange between neighboring Ti atoms, while the role of superexchange is found to be negligible. TiOCl thus is identified as a spin-Peierls system of pure 1D chains of atoms. The first-order character of the transition at T_{c1} is explained by the competition between the structurally deformed state below T_{c2} and the spin-Peierls state below T_{c1}.