Ion gating of the charge density wave order in two-dimensional NbSe₂

Recent experimental advances in atomically thin transition metal dichalcogenide (TMD) metals have unveiled a range of interesting phenomena including the coexistence of charge-density-wave (CDW) order and superconductivity down to the monolayer limit. The atomic thickness of two-dimensional (2D) TMD metals also opens up the possibility for control of these electronic phase transitions by electrostatic gating. Here, with the ionic liquid gate we tune the carrier density in 2D NbSe₂ with the expectation to bring up a CDW phase, which is detailedly characterized with the Raman spectroscopy. We also investigate the variation of CDW order with the change in carrier density and complement phase diagram of 2D NbSe₂, including CDW order and superconducting phase.