Mono-, Bi-, and Tri-layer Charge Density Waves in 1T-TaS2: Direct observation without a substrate
ORAL
Abstract
Charge-density-waves (CDW), which occur 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 [1,2] the direct realspace observation of CDW in mono-layer, bi-layer, and tri-layer 1T-TaS2 crystals using a low voltage scanning-transmission-electron-microscopy (STEM) without a substrate, i.e., free-standing. 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 satisfying the triple q condition q1 + q2 + q3 = 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.
Bilayer crystal clearly shows nearly-commensurate CDW structure. In trilayer crystals, commensurate structure has been observed to be more robust than in the bulk crystal, being stable even at room temperature.
[1] D. Sakabe, Z. Liu, K. Suenaga, K. Nakatsugawa and S. Tanda, npj Quantum Materials, 2, Article number: 22 (2017)
[2] J. Ishioka et. al., Chiral CDW, PRL 105, 176401 (2010)
We report [1,2] the direct realspace observation of CDW in mono-layer, bi-layer, and tri-layer 1T-TaS2 crystals using a low voltage scanning-transmission-electron-microscopy (STEM) without a substrate, i.e., free-standing. 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 satisfying the triple q condition q1 + q2 + q3 = 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.
Bilayer crystal clearly shows nearly-commensurate CDW structure. In trilayer crystals, commensurate structure has been observed to be more robust than in the bulk crystal, being stable even at room temperature.
[1] D. Sakabe, Z. Liu, K. Suenaga, K. Nakatsugawa and S. Tanda, npj Quantum Materials, 2, Article number: 22 (2017)
[2] J. Ishioka et. al., Chiral CDW, PRL 105, 176401 (2010)
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Presenters
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Satoshi Tanda
Department of Applied Physics, Hokkaido University, Hokkaido Univ, Applied Physics, Hokkaido University
Authors
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Satoshi Tanda
Department of Applied Physics, Hokkaido University, Hokkaido Univ, Applied Physics, Hokkaido University
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Zheng Liu
Inorganic Functional Materials Research Institute, AIST
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Kazu Suenaga
National Institute of Advanced Industrial Science and Technology, Nanomaterials Research Institute, AIST, National Institute of Advanced Industrial Science and Technology (AIST)
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Keiji Nakatsugawa
Department of Applied Physics, Hokkaido University, Applied Physics, Hokkaido University