LAUSR

Ion intercalation was recently used to explore two-dimensional (2D) transition metal dichalcogenides (TMDs) with precise tuning of ion concentration in a field-effect-transistor configuration. However, how to systematically change the properties of 2D TMDs, e.g., superconductivity and charge density waves, by ion intercalation has not been explored. We report in this paper results of electrical transport measurements on 2D crystals of $2\text{H}\text{\ensuremath{-}}{\mathrm{TaSe}}_{2}$ intercalated with Li ions that is tuned continuously by ionic gating. Shubnikov--de Haas magnetoconductance oscillation and Hall coefficient measurements on crystals of $2\text{H}\text{\ensuremath{-}}{\mathrm{TaSe}}_{2}$ revealed an ion intercalation induced multi- to single-band change in the Fermi surface (FS) topology, deep in the charge density wave phase, resulting in a reduction of the number of independent channels for electronic conduction. A remarkable crossover from weak antilocalization to weak localization tuned by gate voltage or temperature was found and attributed to the ion intercalation induced variations in the spin-orbital coupling and electron-phonon interaction. These observations provide new insight into the enhancement of superconductivity and the suppression of charge density waves in 2D $2\text{H}\text{\ensuremath{-}}{\mathrm{TaSe}}_{2}$ induced by ion intercalation and demonstrate furthermore the great potential of ion intercalation for engineering electronic properties of 2D TMDs.