Anomalous strain effect in heteroepitaxial SrRuO_(3) films on(111) SrTiO_(3) substrates

We report comprehensive investigations into the structure of high-quality(111)-oriented SrRuO_(3)films on SrTiO_(3)substrates to elucidate the effect of(111)heteroepitaxial strain.We found that SrRuO_(3)film with a thickness of~40 nm is compressively strained in plane on the substrate with full coherency.Nevertheless,the out-of-plane spacing is almost the same as in the bulk,which is at odds with the conventional paradigm.By probing a series of half-order Bragg reflections using synchrotron-based x-ray diffraction combined with analyses of the scanning transmission electron microscopy images,we discovered that the heteroepitaxial strain is accommodated via significant suppression of the degree of c+octahedral tilting and the formation of three equivalent domain structures on the(111)SrTiO_(3)substrate.This anomalous effect sheds light on the understanding of an unconventional paradigm of film-substrate coupling for the(111)heteroepitaxial strain.