Semiconductor-metal phase transition and emergent charge density waves in 1T-ZrX$_2$ (X = Se, Te) at the two-dimensional limit

TL;DR

This study demonstrates a controlled semiconductor-metal phase transition and the emergence of charge density waves in atomically thin 1T-ZrX2 (X=Se, Te) films, revealing simple Fermi surface features and a significant CDW energy gap.

Contribution

It reports the first realization of a dimensionality and intercalation-induced phase transition with CDW order in 1T-ZrX2 ultrathin films, providing new insights into 2D CDW physics.

Findings

Semiconductor-metal phase transition achieved in ultrathin 1T-ZrX2 films.

Observation of a 22 meV CDW energy gap around the Fermi level.

Simplest Fermi surface among known CDW TMDCs, with Zr 4d-derived elliptical electron band.

Abstract

Charge density wave (CDW) is a collective quantum phenomenon in metals and features a wave-like 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 1T-ZrX$_2$ (X = Se, Te) ultra-thin films, accompanied by a commensurate 2 $\times$ 2 CDW order. Furthermore, we observed a CDW energy gap up to 22 meV around the Fermi level. Fourier-transformed scanning tunneling microscopy and angle-resolved photoemission spectroscopy reveal that 1T-ZrX$_2$ films exhibit the simplest Fermi surface among the known CDW materials in TMDCs, consisting only of Zr 4d-derived elliptical electron conduction band at the corners of the Brillouin zone.