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

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.

Automated summary

In this study, aberration-corrected cryogenic transmission electron microscopy (cryo-TEM) was used to investigate the in-and out-of-plane ordering of the commensurate charge density wave (CDW) superstructure in a 1T-TaS2 thin flake. By analyzing the phase intensity variation of modulated Ta atoms, a penetrative 3D CDW stacking structure with an intertwining multidomain structure was visualized, revealing three types of vertical CDW stacking configurations. This research provides microstructural evidence for the coexistence of local Mott insulation and metal phases and offers a paradigm for studying CDW structure and correlation order in condensed-matter physics using cryo-TEM.