Direct Observation of Mono-, Bi-, and Tri-layer Charge Density Waves in 1T-TaS_2 by Transmission Electron Microscopy without a Substrate

Abstract

Charge-density-waves (CDW) which occur mainly in low-dimensional systems have a macroscopic wave function similar to superfluids and superconductors. Kosterlitz-Thouless (KT) transition is observed in superfluids and superconductors, but the presence of KT transition in ultra-thin CDW systems has been an open problem. We report the direct real-space observation of CDWs with new order states in mono-, bi-, and tri-layer 1T-TaS_2 crystal by using a low voltage scanning-transmission-electron-microscope (STEM) without a substrate. This method is ideal to observe local atomic structures and possible defects. We clearly observed that the mono-layer crystal has a new triclinic stripe CDW order without the triple q condition q_1 + q_2 + q_3 = 0. A strong electron-phonon interaction gives rise to new crevasse (line) type defects instead of disclination (point) type defects due to the KT transition. These results reaffirm the importance of the electron-phonon interaction in mono-layer nanophysics.

arXiv comment5 figures, 1 table

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• Zoology of domain walls in quasi-2D correlated charge density wave of 1T-TaS2
• A Unified Picture of Lattice Instabilities in Metallic Transition Metal Dichalcogenides
• A Theoretical Investigation of Charge Density Wave Instability in CuS${}_2$
• Lock-in transition of charge density waves in quasi-one-dimensional conductors: reinterpretation of McMillan's theory
• Photoinduced Dynamics of Commensurate Charge Density Wave in 1T-TaS${}_2$ Based on Three-Orbital Hubbard Model
• Origin of Stripe and Quasi-Stripe CDW Structures in Monolayer MX${}_2$ compounds: Multivalley Free Energy Landscape
• Two-dimensional charge order stabilized in clean polytype heterostructures
• Revisitation of the lock-in transition in one-dimensional charge-density waves