# Ultrafast transient increase of oxygen octahedral rotations in a perovskite

## TL;DR

This study demonstrates that femtosecond photodoping can temporarily enhance oxygen octahedral rotations in EuTiO3, revealing a novel ultrafast structural control mechanism in perovskites with potential for functional state manipulation.

## Contribution

It provides the first evidence of ultrafast photoinduced increase in structural order parameter in a perovskite, linked to charge-transfer effects and tolerance factor reduction.

## Key findings

- Transient increase in oxygen octahedral rotations observed
- Ultrafast charge transfer reduces Goldschmidt tolerance factor
- Structural order parameter enhancement occurs on femtosecond timescales

## Abstract

The ability to control the structure of a crystalline solid on ultrafast timescales bears enormous potential for information storage and manipulation or generating new functional states of matter [1]. In many materials where the ultrafast control of crystalline structures has been explored, optical excitation pushes materials towards their less ordered high temperature phase [2{9] as electronically driven ordered phases melt and possible concomitant structural modifications relax. Nonetheless, for a few select materials it has been shown that photoexcitation can slightly enhance the amplitude of an electronic ordering phenomenon (i.e. its electronic order parameter) [9{13]. Here we show via femtosecond hard X-ray diffraction that photodoping of the perovskite EuTiO3 transiently increases the order parameter associated with a purely structural [14] phase transition represented by the antiferrodistortive rotation of the oxygen octahedra. This can be understood from an ultrafast charge-transfer induced reduction of the Goldschmidt tolerance factor [15], which is a fundamental control parameter for the properties of perovskites