Semiconductor-Metal Phase Transition and Emergent Charge Density Waves in 1<i>T</i>-ZrX<sub>2</sub> (X = Se, Te) at the Two-Dimensional Limit.

Ren, Ming-Qiang; Han, Sha; Fan, Jia-Qi; Wang, Li; Wang, Pengdong; Ren, Wei; Peng, Kun; Li, Shujing et al. · Nano Lett · 2022

basic_science · Level V

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Abstract

A charge density wave (CDW) is a collective quantum phenomenon in metals and features a wavelike modulation of the conduction electron density. A microscopic understanding and experimental control of this many-body electronic state in atomically thin materials remain hot topics in materials physics. By means of material engineering, we realized a dimensionality and Zr intercalation induced semiconductor-metal phase transition in 1<i>T</i>-ZrX<sub>2</sub> (X = Se, Te) ultrathin films, accompanied by a commensurate 2 × 2 CDW order. Furthermore, we observed a CDW energy gap of up to 22 meV around the Fermi level. Fourier-transformed scanning tunneling microscopy and angle-resolved photoemission spectroscopy reveal that 1<i>T</i>-ZrX<sub>2</sub> films exhibit the simplest Fermi surface among the known CDW materials in TMDCs, consisting only of a Zr 4d derived elliptical electron conduction band at the corners of the Brillouin zone.