Based on the refined crystal structure comprised of columns of $3\times 4$ planar blocks of ${\mathrm{NbO}}_6$ octahedra and first principles electronic structure methods, we find that orthorhombic $\left(o\right)\text{−}{\mathrm{Nb}}_{12}{\mathrm{O}}_{29}$ introduces a new class of transition metal oxide. The electronic system consists of a large Nb dimer-based localized orbital comparable in size to those in organometallic compounds, yet is tightly bound and weakly interacting with itinerant electronic bands. These local moments—a rare occurrence for Nb—form one-dimensional spin chains that criss-cross perpendicularly oriented conducting “nanowires.” The local moment bandwidth is comparable to what is seen in rare earth compounds with extremely localized orbitals. The microscopic origin is traced to the local structure of the ${\mathrm{NbO}}_6$ octahedra and associated orbital+spin ordering. The resulting $1{\mathrm{D}}_s\times 1{\mathrm{D}}_c$ anisotropic two dimensional Heisenberg-Kondo lattice model $(s=\text{spin}$; $c=\text{charge})$ provides a strongly anisotropic spin-fermion lattice system for further study.

• Received 14 November 2014
• Revised 13 May 2015

DOI:https://doi.org/10.1103/PhysRevB.91.195152