  The synthesis of new materials with novel or useful properties is one of the
most important drivers in the fields of condensed matter physics and materials
science. Discoveries of this kind are especially significant when they point to
promising future basic research and applications. Van der Waals bonded
materials comprised of lower-dimensional building blocks have been shown to
exhibit emergent properties when isolated in an atomically thin form1-8. Here,
we report the discovery of a transition metal chalcogenide in a heretofore
unknown segmented linear chain form, where basic building blocks each
consisting of two hafnium atoms and nine tellurium atoms (Hf2Te9) are van der
Waals bonded end-to-end. First-principle calculations based on density
functional theory reveal striking crystal-symmetry-related features in the
electronic structure of the segmented chain, including giant spin splitting and
nontrivial topological phases of selected energy band states. Atomic-resolution
scanning transmission electron microscopy reveals single segmented Hf2Te9
chains isolated within the hollow cores of carbon nanotubes, with a structure
consistent with theoretical predictions. Van der Waals-bonded segmented linear
chain transition metal chalcogenide materials could open up new opportunities
in low-dimensional, gate-tunable, magnetic and topological crystalline systems.
