Atomic-scale visualization of the low temperature charge density wave phase in 1T’-TaTe₂

Many transition-metal dichalcogenides, such as TaS₂ and NbSe₂, exhibit charge density wave (CDW) instabilities which, by coupling to the lattice, induce complex periodic lattice displacement patterns. Tellurium-based TMDs further exhibit large electronic and structural anisotropy and significant interlayer correlations. Here, we use cryogenic scanning transmission electron microscopy (STEM) to probe in real space the high temperature (HT) and low temperature (LT) CDW phases in metallic 1T’-TaTe₂. We visualize Ta trimer states at room temperature and observe below the CDW transition temperature (Tc ~ 170 K) the formation of a superstructure arising from complex, periodic intensity modulations in STEM data. The modulations reflect longitudinal periodic lattice displacements that stack in a staggered fashion between the layers. Cross-sectional imaging, density functional theory calculations, and multislice image simulations further elucidate the nature of the HT and LT states. These atomically-resolved measurements reveal the complex role of lattice degrees of freedom in CDW transitions.