Disorder- and Interaction-Driven Quantum Criticality in WSe₂.

Abstract

Quantum fluctuations resulting from strong Coulomb interactions or strong disorders lead to quantum phase transitions (QPTs) in 2D materials. However, understanding of disorder- and interaction-driven QPTs remains a fundamental challenge in 2D materials owing to the presence of strong disorder and strong Coulomb interactions. Here, we study the systematic interplay of strong disorder and strong Coulomb interactions by controlling the thickness of WSe₂ to elucidate the disorder- and interaction-driven metal-insulator QPTs. An observation of metal-insulator transitions (MITs) with a conductivity of ∼<i>e</i>²/<i>h</i> in thin-WSe₂ agrees with the Mott-Ioffe-Regel limit, excluding bad-metal behavior; conversely, MITs with a conductivity of <<i>e</i>²/<i>h</i> demonstrate the bad-metal behavior in thick-WSe₂. We observe the distinct temperature dependences of resistivity, which unveil anomalous metallic transport in WSe₂. Furthermore, the emergence of the metallic glass phase (MGP) in thin-WSe₂ underscores the significant role of strong disorder and strong Coulomb interactions. Contrarily, the absence of the MGP in thick-WSe₂ suggests that the Coulomb interactions dominate over the disorder. Finally, the successful scaling collapse of conductivity reveals the disorder-dominated quantum criticality in thin-WSe₂ and interaction-driven Mott quantum criticality in thick-WSe₂. This study provides compelling evidence that thickness-dependent WSe₂ could be an exciting testbed to understand anomalous metallic transport and metal-insulator QPTs in 2D materials.