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arXiv · 1707.06890

Strain Engineering a $4a\times\sqrt{3}a$ Charge Density Wave Phase in Transition Metal Dichalcogenide 1T-VSe$_2$

Duming Zhang·Jeonghoon Ha·Hongwoo Baek·Yang-Hao Chan·Fabian D. Natterer·Alline F. Myers·Joshua D. Schumacher·William G. Cullen·Albert V. Davydov·Young Kuk·M. Y. Chou·Nikolai B. Zhitenev·Joseph A. Stroscio
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Abstract

We report a rectangular charge density wave (CDW) phase in strained 1T-VSe$_2$ thin films synthesized by molecular beam epitaxy on c-sapphire substrates. The observed CDW structure exhibits an unconventional rectangular 4a{\times}{\sqrt{3a}} periodicity, as opposed to the previously reported hexagonal $4a\times4a$ structure in bulk crystals and exfoliated thin layered samples. Tunneling spectroscopy shows a strong modulation of the local density of states of the same $4a\times\sqrt{3}a$ CDW periodicity and an energy gap of $2Δ_{CDW}=(9.1\pm0.1)$ meV. The CDW energy gap evolves into a full gap at temperatures below 500 mK, indicating a transition to an insulating phase at ultra-low temperatures. First-principles calculations confirm the stability of both $4a\times4a$ and $4a\times\sqrt{3}a$ structures arising from soft modes in the phonon dispersion. The unconventional structure becomes preferred in the presence of strain, in agreement with experimental findings.

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Duming Zhang, Jeonghoon Ha, Hongwoo Baek, Yang-Hao Chan, Fabian D. Natterer, Alline F. Myers, Joshua D. Schumacher, William G. Cullen, Albert V. Davydov, Young Kuk, M. Y. Chou, Nikolai B. Zhitenev, Joseph A. Stroscio. 2017-07-20. Strain Engineering a $4a\times\sqrt{3}a$ Charge Density Wave Phase in Transition Metal Dichalcogenide 1T-VSe$_2$. https://doi.org/10.1103/physrevmaterials.1.024005

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