Investigation on minimal Hamiltonian for system of material with highly anisotropic transport and optical properties SrNbO3.4

A recent experimental study on Sr1−yNbO3+δ revealed that the material has very high anisotropy in its transport and optical response characteristics. The material behaves as a conductor along a crystal axis, but as an insulator along b and c crystal axes. We hypothesize that the strong anisotropy occurs because of the unique arrangement of orbitals of certain atoms around the Fermi level. To find out the most contributing orbitals, we do density functional theory (DFT) calculation and map the results to construct a multi-band tight-binding Hamiltonian. We remove the orbitals that have low contribution to the main feature of the band structure around the Fermi level, until we obtain a minimal Hamiltonian that still carries the strong anisotropic characteristic. Our results reveal that the d orbitals of Nb atoms in the interfaces, O atoms between Nb, and the crystal structure of SrNbO3.4 itself determine the anisotropic characteristic of the transport and optical properties of the material.