Evidence of nested quasi-one-dimensional Fermi surface and decoupled charge-lattice orders in layered TaTe 2

The formations of charge and lattice orders are generally coupled in charge density wave (CDW) materials and share identical order wave vectors. Although this situation is usually satisfied in a large class of two-dimensional materials, it falls short in describing the so-called CDW-like phase transition in layered tantalum ditelluride (TaTe2), accompanied by anomalous low temperature transport properties and a periodic lattice distortion (PLD). Here we combine angle-resolved photoemission spectroscopy and low energy electron diffraction to directly access the charge and lattice structures in 1T-polytypic TaTe2 and study the anomalous phase transition. Our data reveal the presence of a surprising quasi-one-dimensional Fermi surface with nesting (FSN) condition, despite its van der Waals layered structure. We find that the wave vectors of the FSN and PLD are different, suggesting the decoupled formation between charge and lattice orders. These conditions are accompanied by rich footprints in band structure, including Fermi surface suppression, minigaps, and satellite bands. Our results suggest that TaTe2 manifests intrinsic mixed dimensionality between its electronic and lattice structure and that the CDW-like phase transition is likely governed by multiple mechanisms. Our work provides routes for forging unconventional CDW phases and charge-lattice entanglement that would otherwise not be available in materials with fixed dimensionality.