Unusual charge density wave introduced by the Janus structure in monolayer vanadium dichalcogenides.

As a fundamental structural feature, the symmetry of materials determines the exotic quantum properties in transition metal dichalcogenides (TMDs) with charge density waves (CDWs). The Janus structure, an artificially constructed lattice, provides an opportunity to tune the electronic structures and their associated behavior, such as CDW states. However, limited by the difficulties in atomic-level fabrication and material stability, the experimental visualization of the CDW states in two-dimensional (2D) TMDs with Janus structure is still rare. Here, using surface selenization of VTe(2), we fabricated monolayer Janus VTeSe. With scanning tunneling microscopy, we observed and characterized an unusual [Formula: see text] CDW state with threefold rotational symmetry breaking. Combined with theoretical calculations, we find that this CDW state can be attributed to the magnetic-involved charge modulation in the Janus VTeSe, rather than the conventional electron-phonon coupling. Our findings provide a promising platform for studying the CDW states and artificially tuning the electronic properties of the 2D TMDs toward the related fundamental and applied studies.