Sample independence of magnetoelastic excitations in the rare earth pyrochlore Tb2Ti2O7

TL;DR

This study investigates the magnetoelastic excitations in Tb2Ti2O7, revealing that these excitations are independent of structural disorder and highlighting complexities in comparing different sample types.

Contribution

It demonstrates that magnetoelastic coupling in Tb2Ti2O7 is unaffected by structural disorder and clarifies the differences between single crystal and powder samples.

Findings

Magnetoelastic excitations are independent of structural disorder.

Sample type influences the correlation between lattice parameters and thermodynamic features.

Comparison between single crystal and powder samples is more complex than previously assumed.

Abstract

Recent experimental results have emphasized two aspects of Tb2Ti2O7 which have not been taken into account in previous attempts to construct theories of Tb2Ti2O7: the role of small levels of structural disorder, which appears to control the formation of a long-range ordered state of as yet unknown nature; and the importance of strong coupling between spin and lattice degrees of freedom, which results in the hybridization of crystal field excitons and transverse acoustic phonons. In this work we examine the juncture of these two phenomena and show that samples with strongly contrasting behavior vis-a-vis the structural disorder (i.e. with and without the transition to the ordered state), develop identical magnetoelastic coupling. We also show that the comparison between single crystal and powder samples is more complicated than previously thought - the correlation between lattice parameter (as a measure of superstoichiometric Tb$^{3+}$) and the existence of a specific heat peak, as observed in powder samples, does not hold for single crystals.