Electric field effect on the charge density wave in the quasi-one-dimensional semimetal Ta2Ni Se7

The charge density wave (CDW) instability often requires the participation of electron density of state at the Fermi level for the electronic energy gain in the structurally modulated phase, whether it is due to Fermi surface nesting (FSN) or the electron-phonon coupling mechanism. The physics of the CDW in the quasi-one-dimensional semimetal Ta2NiSe7 remains elusive for the lack of consistent Fermi surface response in the CDW state. Here, we investigate the electric-field effect in the CDW state in Ta2NiSe7 using ionic liquid gated field-effect transistors (iFETs) fabricated based on 10-20-nm-Thick flakes. The strong electric field at the ionic liquid/flake interface and low carrier density in Ta2NiSe7 facilitate a finite electric-field response in the CDW state. The onset temperature of CDW shows a nearly negligible electric field dependence, whereas the resistivity shows a sizeable tunability: The resistivity increases at positive gating in the normal state but decreases in the CDW state instead. Our first-principles calculations revealed nested holelike Fermi surfaces with a nesting vector weakly coupled with electric-field gating and a nesting area increasing more significantly in a negative electric gating than in a positive electric gating. The calculated Fermi surfaces provide an adequate account for the intricate transport in Ta2NiSe7, which indicates the dominant role of FSN in the CDW mechanism under current debate in this system.