Disorder- and Interaction-Dominated Quantum Criticalities in WSe₂

Quantum fluctuations owing to strong Coulomb interactions or strong disorder lead to quantum phase transition (QPT) in 2D systems. However, understanding of disorder- and interaction-driven QPTs remains a fundamental challenge in condensed matter physics. Here, we use thickness-dependent WSe₂ to elucidate the quantum phase metal-insulator transition driven by strong disorder, and strong Coulomb interactions in thin- and thick-WSe₂, respectively. An observation of crossover conductance ~e²/<i>h</i> signifies the role of quantum fluctuations due to strong disorder in bi- and five-layer WSe₂. In contrary, the crossover conductance ~0.1 e²/<i>h</i> demonstrates bad-metal behavior associated with Mott quantum criticality owing to strong Coulomb interactions in ten-layer WSe₂. In the metallic phase, resistivity (<i>ρ</i>) follows Fermi-liquid (<i>ρ</i> ∝ <i>T</i>²) and non-Fermi-liquid (<i>ρ</i> ∝ <i>T</i>^1.5) behaviors in bi- and five-layer WSe₂ from low to high temperatures, respectively. In ten-layer WSe₂, <i>ρ </i>displays a <i>T</i>²-dependence at low temperatures while it shows a <i>T-</i>linear behavior at moderate temperatures in the deep metallic phase, suggestive of strange-metal behavior. Further, the strange-metal transforms into the bad-metal around the crossover point in ten-layer WSe₂. Moreover, conductivity (<i>σ</i>) exhibits a <i>T</i>-dependence as δ<i>σ</i> ∝ <i>T</i>^3/2 in the vicinity of critical point, suggesting the metallic glass phase which highlights the significant role of strong disorder and Coulomb interactions in bi- and five-layer WSe₂ devices. The absence of such a phase in ten-layer WSe₂ attributes that the Coulomb interactions dominate over disorder in ten-layer WSe₂. Critical scaling of conductivity as a function of temperature and carrier density reveals the disorder-dominated quantum criticality in bi- and five-layer WSe₂, and interaction-dominated quantum criticality in ten-layer WSe₂. This study provides compelling evidence that thickness-dependent WSe₂ serves as a new platform to study the disorder- and interaction-dominated QPTs in 2D systems.