Flatbands in frustrated lattice X3MnN3 (X = Ca, Sr, Ba): A first-principles study

Frustrated lattices with dispersionless band structures and fully localized states are an exciting platform for exploring many-body physics. In this work, we identify X3MnN3 ( X = Ca, Sr, Ba) as a frustrated lattice and investigate its physical properties in the ferromagnetic (FM) and antiferromagnetic (AFM) states based on first-principles calculations. Our results show that all three materials in FM and A-type AFM configurations have flatbands with band touching in the k(z)0 and k(z)p planes with bandwidths less than 0.2 eV. Intriguingly, the flatband is tuned to the Fermi level when X3MnN3 is transformed into the FM state. Furthermore, we find the two-dimensional dice model hidden in X3MnN3 by treating the coupled Mn and N atoms as a basic site, revealing that the compact localized state is generated by destructive interferences between the hopping amplitudes, and the dice models stack the system staggered along the c-axis. Our work provides new candidate materials for exploring strong correlation physics and reveals the mechanism of their localized state.