Zhang, DumingHa, JeonghoonBaek, HongwooChan, Yang-HaoNatterer, Fabian D.Myers, Alline F.Schumacher, Joshua D.Cullen, William G.Davydov, Albert V.Kuk, YoungChou, M. Y.Zhitenev, Nikolai B.Stroscio, Joseph A.2018-01-152018-01-152018-01-15201710.1103/PhysRevMaterials.1.024005https://infoscience.epfl.ch/handle/20.500.14299/143948WOS:000416557400002We 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 x root 3a periodicity, as opposed to the previously reported hexagonal 4a x 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 x root 3a CDW periodicity and an energy gap of 2 Lambda(CDW) = (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 x 4a and 4a x root 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.text::journal::journal article::research article