Elastic anomaly for Sr Ti O 3 thin films grown on Si(001)

X-ray diffraction measurements have revealed a negative Poisson's ratio for $\mathrm{Sr}\mathrm{Ti}{\mathrm{O}}_{3}$ thin films grown on Si(001). X-ray absorption fine-structure measurements demonstrate that this elastic anomaly is driven by the interfacial polarization of the $\mathrm{Sr}\mathrm{Ti}{\mathrm{O}}_{3}$ layers. First-principles density-functional calculations support these conclusions. It is suggested that this phenomenon may be common for heteroepitaxial growth of materials that possess an ionic polarizability.