Strain propagation in nanolayered perovskites probed by ultrafast x-ray diffraction

Abstract

Strain propagation in a perovskite heterostructure grown on a ${\mathrm{SrTiO}}_{3}$ (STO) substrate is studied by ultrafast x-ray diffraction. Femtosecond displacive phonon excitation in a ${\mathrm{PbZr}}_{0.2}{\mathrm{Ti}}_{0.8}{\mathrm{O}}_{3}∕{\mathrm{SrRuO}}_{3}$ (PZT/SRO) film launches acoustic strain waves propagating into the STO substrate. We demonstrate a two-step time evolution of diffracted x-ray intensity which originates from different interfering contributions to the (004) Bragg peak of the STO substrate. Analysis by dynamical x-ray diffraction theory gives the absolute strain $\mathrm{\ensuremath{\Delta}}a∕{a}_{0}$ in a wide range of optical pump fluences. Ultrafast transient strain as small as $\mathrm{\ensuremath{\Delta}}a∕{a}_{0}=2\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}5}$ is determined in this way.