We report a rectangular charge density wave (CDW) phase in strained 1T-VSe2 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×4a 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×3a CDW periodicity and an energy gap of 2ΔCDW=(9.1±0.1) 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×4a and 4a×3a structures arising from soft modes in the phonon dispersion. The unconventional structure becomes preferred in the presence of strain, in agreement with experimental findings.
@article{arxiv.1707.06890,
title = {Strain Engineering a $4a\times\sqrt{3}a$ Charge Density Wave Phase in Transition Metal Dichalcogenide 1T-VSe$_2$},
author = {Duming Zhang and Jeonghoon Ha and Hongwoo Baek and Yang-Hao Chan and Fabian D. Natterer and Alline F. Myers and Joshua D. Schumacher and William G. Cullen and Albert V. Davydov and Young Kuk and M. Y. Chou and Nikolai B. Zhitenev and Joseph A. Stroscio},
journal= {arXiv preprint arXiv:1707.06890},
year = {2017}
}