Charge ordering at the interface in (LaMnO$_3$)$_{2n}$/(SrMnO$_3$)$_n$   superlattices as the origin of their insulating state
  We have performed ab initio calculations within the LDA+U method in the multilayered system (LaMnO$_3$)$_{2n}$ / (SrMnO$_3$)$_n$. Our results suggest a charge-ordered state that alternates Mn$^{3+}$ and Mn$^{4+}$ cations in a checkerboard in-plane pattern is developed at the interfacial layer, leading to a gap opening. Such an interfacial charge-ordered situation would be the energetically favored reconstruction between LaMnO$_3$ and SrMnO$_3$. This helps understanding the insulating behavior observed experimentally in these multilayers at intermediate values of $n$, whose origin is known to be due to some interfacial mechanism. 
Victor Pardo, Antia S. Botana, Daniel Baldomir
cond-mat.str-el cond-mat.mtrl-sci