Effect of strain and electric field on the electronic soft matter in manganite thin films

We have studied the effect of substrate-induced strain on the properties of thin films of the hole-doped manganite ${({\mathrm{La}}_{1\ensuremath{-}y}{\mathrm{Pr}}_{y})}_{0.67}{\mathrm{Ca}}_{0.33}\mathrm{Mn}{\mathrm{O}}_{3}$ ($y=0.4$, 0.5, and 0.6) grown on $\mathrm{Nd}\mathrm{Ga}{\mathrm{O}}_{3}$ (NGO) substrates, in order to distinguish between the roles played by long-range strain interactions and quenched atomic disorder in forming the micrometer-scale phase separated state. We show that a fluid phase separated (FPS) state is formed at intermediate temperatures similar to the strain-liquid state in bulk compounds, which can be converted to a metallic state by applying an external electric field. In contrast to bulk compounds, at low temperatures a strain stabilized ferromagnetic metallic (FMM) state is formed in the $y=0.4$ and 0.5 samples. However, in the $y=0.6$ sample a static phase separated (SPS) state is formed similar to the strain-glass phase in bulk compounds. Our results suggest that the substrate-induced strain is a function of temperature. Hence, we show that the temperature induced variation of the long-range strain interactions plays a dominant role in determining the properties of thin films of phase-separated manganites.