The SrTiO$_3$ displacive transition revisited by Coherent X-ray Diffraction

TL;DR

This study uses Coherent X-ray Diffraction to analyze the complex phase transition in SrTiO$_3$, revealing spatially distinct static and dynamic components associated with different length scales and their relation to known fluctuation phenomena.

Contribution

It provides a detailed spatial and temporal characterization of the two length scale components in SrTiO$_3$'s phase transition using coherent X-ray diffraction, linking static domains and slow dynamics.

Findings

Disentangled short- and long-length scale components spatially.

Identified static ordered domains via speckle patterns.

Linked broad component speckles to slow dynamical processes.

Abstract

We present a Coherent X-ray Diffraction study of the antiferrodistortive displacive transition of SrTiO$_3$, a prototypical example of a phase transition for which the critical fluctuations exhibit two length scales and two time scales. From the microbeam x-ray coherent diffraction patterns, we show that the broad (short-length scale) and the narrow (long-length scale) components can be spatially disentangled, due to 100 $\mu$m-scale spatial variations of the latter. Moreover, both components exhibit a speckle pattern, which is static on a $\sim$10 mn time-scale. This gives evidence that the narrow component corresponds to static ordered domains. We interpret the speckles in the broad component as due to a very slow dynamical process, corresponding to the well-known \emph{central} peak seen in inelastic neutron scattering.