Analysis of the phonon spectrum in the titanium oxyhalide TiOBr

TL;DR

This study investigates the phonon spectrum and electrodynamic response of TiOBr, revealing extended fluctuations, spin-gap formation, and electron-phonon interactions, with comparisons to related oxyhalides highlighting effects of dimensionality.

Contribution

It provides the first detailed analysis of phonon anomalies and fluctuation regimes in TiOBr, emphasizing the role of dimensionality and interplane coupling.

Findings

Extended fluctuation regime above T_C1

Progressive suppression of spectral weight at low frequencies

Correlation between phonon parameters and magnetic susceptibility

Abstract

We present the electrodynamic response of TiOBr, which undergoes a transition to a spin-singlet ground state for temperatures below T$_{C1}=28$ K. The temperature evolution of the phonon anomalies indicates, like in \cl, an extended fluctuation regime, extending well above T$_{C1}$. At low frequencies, the spectral weight is progressively suppressed by decreasing the temperature, suggesting the formation of a spin-gap and a considerable electron-phonon coupling. A comparison of the two oxyhalides shows a weaker interplane coupling and reduced dimensionality for TiOBr that enhances fluctuations and shifts the ordering temperatures to lower values. In the fluctuation regime the temperature dependencies of some phonon parameters track the temperature evolution of the magnetic susceptibility.