Fig. 1
The cleaved calcium ruthenate surface. a Unit cell of the n = 2 member of the Can+1RunO2n+1 Ruddlesden Popper series. The crystal cleaves easily between neighboring CaO layers (marked by gray planes). b Top view of the CaO-terminated Ca3Ru2O7(001) surface. The RuO6 octahedra are alternately tilted with respect to the c axis (most pronounced in the ac plane), and rotated in the ab plane as indicated by the straight and curved arrows, respectively. The red box marks the orthorhombic unit cell (a = 5.365 Å, b = 5.562 Å). c STM image of the cleaved surface. The dark (bright) lines along the [010] direction correspond to areas where the apical oxygen atoms of the RuO6 octahedra are tilted toward (away from) each other (see panel d). The point defects are attributed to spurious impurities (see SI). The scale bar corresponds to 3 nm. STM parameters: T sample = 78 K, V sample = +0.8 V, I tunnel = 0.1 nA; image rotated and cropped; fast scan direction is 68° clockwise from horizontal. d Tersoff-Hamann simulation of the cleaved surface
