Low-Temperature Transport Measurements of Multilayer WSe$_{2}$ FETs

Transition metal dichalcogenides (TMDs) offer an exciting new opportunity to study transport in 2D and the universality of the 2D metal-insulator-transition (MIT), but high-resistance, non-ohmic contacts have been a major impediment. Recently, however, 2D/2D low-resistance ohmic contacts have been produced on ultrathin TMD samples [1] allowing for low-temperature characterization. We report studies of WSe$_2$ FET samples with $\sim 10$ layers each, patterned into Hall bars, and with a favorably high mobility of up to $\sim 0.2$~m$^2/$Vs at $\sim 5$~K. Two-terminal and four-terminal conductivity ($\sigma$) measurements were performed at temperatures $0.25\leq T$(K)$<200$. Our results show that contacts remain ohmic down to 0.25~K over the entire useful range of back-gate voltages $V_{bg}$. Furthermore, the measurements reveal a change in the sign of $ d\sigma/dT $ and the form of $\sigma(T)$ with $V_{bg}$, strongly suggesting the existence of a 2D MIT in this system. [1] Hsun-Jen~Chuang \textit{et al.}, Nano Lett. \textbf{16}, 1896 (2016).