Metal-insulator transition at low densities in a two-dimensional low-bandgap semiconductor.

Abstract

Metal-insulator transitions in low band-gap systems emerge from the interplay of interactions, disorder, and band structure on comparable energy scales. Platinum diselenide, with its thickness-dependent electronic structure, provides an ideal platform to explore this regime, as the five-layer limit lies close to the semimetallic boundary while retaining a small bandgap (~0.1 eV). Here we show that hexagonal boron nitride-encapsulated five-layer PtSe₂ devices with embedded ultra-flat, pre-patterned platinum contacts exhibit high electronic quality, with mobilities up to 1,640 cm²V^-1s^-1 and contact resistances as low as 1.31 kΩ·μm at 1.5 K. These characteristics enable a gate-tunable metal-insulator transition at carrier densities down to 2.75 × 10¹⁰ cm⁻². Transport in this regime is dominated by electron-electron interactions, as supported by finite-temperature scaling. Below 50 K, however, an additional disorder-related energy scale emerges, consistent with percolation. These results demonstrate that disorder remains relevant even in high-mobility devices, challenging a purely interaction-driven transition in two-dimensional systems.