Soft-mode-mediated coherent semiconductor–metal transition in ReS2 induced by charge doping

Abstract

Phase engineering is pivotal for tailoring the properties of materials, enabling on-demand modulation of their physical properties. Two-dimensional transition-metal dichalcogenides (2D-TMDs) exemplify this potential, as their diverse polymorphs can be selectively stabilized to satisfy specific application requirements. Among them, ReS₂ naturally crystallizes in the 1T″ phase and exhibits pronounced in-plane anisotropy, offering unique opportunities for anisotropic electronic applications. Here, based on density functional theory (DFT) calculations, we report a hole-injection-driven phase transition from the semiconducting 1T″ phase to the metallic 1T′ phase in ReS₂. We find that hole doping stabilizes the metastable 1T′ phase and renders it energetically favorable. Ab initio molecular dynamics simulations further reveal the 1T″–1T′ transition dynamics, showing that a stable transition occurs at a doping level of approximately 9.5 × 10¹⁴ cm⁻². The underlying mechanism is attributed to the hole-doping-induced reshaping of the potential energy surface (PES), whereby the structure at the PES minimum gradually converges to the 1T′ configuration with increasing doping. The directional driving force generated by this PES evolution manifests as collective atomic displacements along coherent-phonon coordinates. The phase transition proceeds predominantly along the eigenvectors of two soft phonon modes in the doped 1T″ phase. This work establishes a microscopic framework for the semiconductor–metal transition in ReS₂ under hole doping and offers new avenues for phase-controlled crystal engineering toward advanced electronic applications.