Insulator-to-Metal Phase Transition in a Few-Layered 2D Semiconductor Field Effect Transistor

Metal-to-insulator phase transition (MIT) in low dimensional materials and particularly two-dimensional layered semiconductors is exciting to explore due to the fact that it challenges the

prediction of Abrahams et al. [PRL 42, 673 (1979)] that a two-dimensional system must be insulating at low temperatures. Thus, the exploration of MITs in 2D layered semiconductors expands the understanding of the underlying physics. Here I will discuss the MIT of few layered 2D semiconducting material such as MoS₂, ReS₂ and our recently explored MoSe₂ field effect transistor under a gate bias (electric field) applied perpendicularly to the layers. Under low applied gate voltage, the conductivity as a function of temperature on these 2D semiconductor shows typical semiconducting behavior and above a critical applied gate voltage (V_c), the conductivity becomes metallic i.e., the conductivity increases continuously as a function of decreasing temperature. Evidence of a metallic state was observed using an applied gate voltage or, equivalently, increasing the density of charge carriers within the 2D channel. We explored the nature of the phase transition using Quantum Phase Transition as well as percolation theory, which I will discuss in detail.