Sample independence of magnetoelastic excitations in the rare-earth pyrochlore Tb2Ti2 O7

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 the lattice parameter (as a measure of superstoichiometric Tb3+) and the existence of a specific heat peak, as observed in powder samples, does not hold for single crystals.