Charge density wave order, local lattice distortions, and topological electronic states in NbTe4

Assessing the atomic and electronic structure of strongly correlated systems in which the crystal symmetry changes due to emergent lattice distortions, such as charge density waves (CDWs), is nontrivial because the distortions are not necessarily amenable to a traditional crystallographic description. Using advance scattering and modeling techniques, we reveal the evolution of the atomic displacement modes behind the CDW phases of quasi-one-dimensional NbTe4 and derive the so far unknown atomic structure of its low-temperature commensurate (C) CDW phase. Electronic structure calculations based on the experimental C-CDW structure data predict the existence of Dirac fermions whose multiplicity turns out to depend on the degree of lattice distortions accounted for in the experimental structure derivation. We argue that the electronic structure of CDW systems in general, and in particular in transition metal tetratellurides, can be strongly impacted by local lattice distortions and, therefore, they should be fully accounted for when their rich physics is considered.