Atomic Visualization of the 3D Charge Density Wave Stacking in 1T-TaS₂ by Cryogenic Transmission Electron Microscopy

Abstract

Charge density waves (CDWs) in 1T-TaS2 maintain 2D ordering by forming periodic in-plane star-of-David (SOD) patterns, while they also intertwined with orbital order in the c axis. Recent theoretical calculations and surface measurements have explored 3D CDW configurations, but interlayer intertwining of a 2D CDW order remains elusive. Here, we investigate the in- and out-of-plane ordering of the commensurate CDW superstructure in a 1T-TaS2 thin flake in real space, using aberration-corrected cryogenic transmission electronic microscopy (cryo-TEM) in low-dose mode, far below the threshold dose for an electron-induced CDW phase transition. By scrutinizing the phase intensity variation of modulated Ta atoms, we visualize the penetrative 3D CDW stacking structure, revealing an intertwining multidomain structure with three types of vertical CDW stacking configurations. Our results provide microstructural evidence for the coexistence of local Mott insulation and metal phases and offer a paradigm for studying the CDW structure and correlation order in condensed-matter physics using cryo-TEM.

Stacking and spin order in a van der Waals Mott insulator 1T-TaS2

“…1c(d). In recent transmission electron microscopy, stacking faults other than the AC stacking order were observed in a thin flake 16 . However, the thin flakes were differentiated from the bulk 16 , and both electron microscopy and X-ray diffraction measurements confirmed a well-ordered AC stacking structure in bulk samples 11,15 .…”

“…In recent transmission electron microscopy, stacking faults other than the AC stacking order were observed in a thin flake 16 . However, the thin flakes were differentiated from the bulk 16 , and both electron microscopy and X-ray diffraction measurements confirmed a well-ordered AC stacking structure in bulk samples 11,15 . Nevertheless, we further considered the B stacking as a stacking fault and there can be B stacking cases in both type-I and type-II terminations as shown in the figure.…”

Cryogenic transmission electron microscopy on beam-sensitive materials and quantum science

“…HRTEM was then performed using a Cryo-TEM with a DDEC camera that minimizes electron beam damage. [119] The Cryo-TEM's integrated cold stage design minimizes vibrations, further enhancing image stability. Crucially, the DDEC camera's electron counting mode reduces damage to the material's intrinsic CDW structure.…”

Engineering Charge Density Waves by Stackingtronics in Tantalum Disulfide

“…Interlayer van der Waals (vdW) coupling with associated periodic lattice distortions (PLDs) predominantly governs the CDW order in layered 2D materials . Transition metal dichalcogenides, such as TaS 2 , TaSe 2 , NbSe 2 , or other transition metal dichalcogenides (TMDs), are typical CDW systems that spontaneously break lattice symmetry through PLDs. CDW, a series of unusual charge-ordered states in low-dimensional phenomena, can be explained by the conventional Peierls mechanism via the Fermi-surface nesting (FSN) in one-dimensional form. , However, when the system transitions to two dimensions, FSN is no longer sufficient to account for the origin of the CDW.…”