Atomic and electronic structure of the YBa2Cu3O7/SrTiO3 interface from first principles

The atomic structure, adhesion energy, and bonding nature of the YBa2Cu3O7(001)/SrTiO3 (00 1) interface are systematically investigated from first principles. A total of 48 candidate interface geometries, which involve two SrTiO3 terminations, six YBa2Cu3O7 terminations, and four highly symmetric stacking sequences. were considered. Although the SrTiO3 substrate has a negligible effect on the atomic structure of optimal TiO2-terminated interface, its electronic influence is significant: the electronic states of interfacial O of YBa2Cu3O7 resemble those of O in bulk SrTiO3 rather than bulk YBa2Cu3O7-Consequently, the interfacial O of YBa2Cu3O7 can be reasonably regarded as a natural extension of substrate layer across the interface. However, the effect of substrate on the optimal SrO-terminated interface is twofold characterized atomically by straightening the originally zigzag interfacial YBa2Cu3O7 layer and electronically by altering noticeably the density of states projected oil this layer. In addition, the substrate is found to affect the interface chemistry via tuning effectively the first monolayer of the YBa2Cu3O7 film. The preferred geometries (i.e., having the largest adhesion energy) are those that maintain the substrate perovskite stacking across the interface. By applying several methods of analysis, we thoroughly characterized electronic structure and determined that interfacial bonding is mainly ionic, yet maintains a small degree of covalency. (C) 2009 American Institute of Physics. [doi: 10.1063/1.3257264]