||Direct observation of mono-layer, bi-layer, and tri-layer charge density waves in 1T-TaS2 by transmission electron microscopy without a substrate
Sakabe, Daiki ,
Liu, Zheng ,
Suenaga, Kazutomo ,
Nakatsugawa, KeijiTanda, Satoshi
6 , 2017-04-25 , Nature Publishing Group
Charge-density-waves, which occur mainly in low-dimensional systems, have a macroscopic wave function similar to superfluids and superconductors. Kosterlitz-Thouless transition is observed in superfluids and superconductors, but the presence of Kosterlitz-Thouless transition in ultra-thin charge-density-waves systems has been an open problem. We report the direct real-space observation of charge-density-waves with new order states in mono-layer, bi-layer, and tri-layer 1T-TaS2 crystals using a low voltage scanning-transmission-electron-microscopy 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 charge-density-waves order without satisfying 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 Kosterlitz-Thouless transition. These results reaffirm the importance of the electron-phonon interaction in mono-layer nanophysics.