Incommensurate spin Luttinger liquid phase in a model for the spin-Peierls materials TiOBr and TiOCl

TL;DR

This paper models the incommensurate phase of spin-Peierls materials TiOBr and TiOCl, revealing a Luttinger liquid-like behavior with gapless excitations and incommensurate correlations, aligning with experimental observations.

Contribution

It introduces a simple elastic model of spin chains on a triangular lattice that captures phase transitions and incommensurate behavior in TiOX compounds.

Findings

Reproduces uniform-incommensurate and incommensurate-dimerized phase transitions

Predicts gapless spin excitations in the incommensurate phase

Shows incommensurate spin correlations consistent with Luttinger liquid behavior

Abstract

In the present work we aim to characterize the lattice configurations and the magnetic behavior in the incommensurate phase of spin-Peierls systems. This phase emerges when the magnetic exchange interaction is coupled to the distortions of an underlying triangular lattice and has its experimental realization in the quasi-one dimensional compound family TiOX (X = Cl, Br). With a simple model of spin-1/2 chains inserted in a planar triangular geometry which couples them elastically, we are able to obtain the uniform-incommensurate and incommensurate-dimerized phase transitions seen in these compounds. Moreover, we follow the evolution of the wave-vector of the distortions with temperature inside the incommensurate phase. Finally, we predict gapless spin excitations for the intermediate phase of TiOX compounds along with incommensurate spin-spin correlations. This exotic Luttinger liquid-like behavior could be observed in future experiments.