Low temperature and high pressure Raman and x-ray studies of pyrochlore Tb$_2$Ti$_2$O$_7$ : phonon anomalies and possible phase transition

TL;DR

This study investigates how temperature and pressure affect the phonon behavior and structure of Tb$_2$Ti$_2$O$_7$, revealing anharmonic interactions and a potential phase transition relevant to its spin-liquid properties.

Contribution

It provides a detailed analysis of phonon anomalies and structural deformation in Tb$_2$Ti$_2$O$_7$ under varying conditions, combining Raman and x-ray techniques for the first time.

Findings

Anomalous temperature dependence of phonons due to anharmonic interactions

Quantitative estimates of phonon frequency changes using Grüneisen parameters

Evidence of structural deformation at around 9 GPa

Abstract

We have carried out temperature and pressure-dependent Raman and x-ray measurements on single crystals of Tb$_2$Ti$_2$O$_7$. We attribute the observed anomalous temperature dependence of phonons to phonon-phonon anharmonic interactions. The quasiharmonic and anharmonic contributions to the temperature-dependent changes in phonon frequencies are estimated quantitatively using mode Gr\"{u}neisen parameters derived from pressure-dependent Raman experiments and bulk modulus from high pressure x-ray measurements. Further, our Raman and x-ray data suggest a subtle structural deformation of the pyrochlore lattice at $\sim$ 9 GPa. We discuss possible implications of our results on the spin-liquid behaviour of Tb$_2$Ti$_2$O$_7$.