Analysis of Screening Mechanisms for Polar Discontinuity for LaAlO3/SrTiO3 Thin Films Based on Ab initio Calculations

We perform a systematic study of electronic structures and potential profiles based on the ab initio calculations for LaAlO3/SrTiO3 (001)-stacking thin films [(TiO2-SrO)(2)(AlO2-LaO)(n) and (SrO-TiO2)(2)(LaO-AlO2)(n) (n = 1, 2, 3,4,5)] with and without atomic position relaxation. To eliminate artifacts from periodic boundary condition, the exact Coulomb cutoff technique [Rozzi et al.: Phys. Rev. B 73 (2006) 205119] is applied. Without atomic position relaxation, the system is a metal for all the 10 cases. In contrast, with atomic position relaxation, systems with n <= 3 have finite band gaps though those with n = 4,5 are metals. However, careful inspection reveals that, even for n = 4 and 5, the n-type interface (LaO-TiO2) is conducting while the p-type interface (SrO-AlO2) is insulating. Screening mechanisms are discussed for cases with and without atomic position relaxation.