Anomalous polarization evolution associated with pressure-induced topological transitions in black phosphorus

The fundamental interplay between pressure-driven electronic transitions and anisotropic optical responses remains unresolved in layered black phosphorus (BP), particularly regarding polarization-selective signatures under compression. By deploying high-pressure angle-resolved polarized Raman spectroscopy, we systematically investigate the pressure-induced optical anisotropy characterized by the effective Raman tensor element ratio of Ag modes from bulk to atomically thin BP flakes. Under hydrostatic compression, two reversals in the Raman tensor element ratio are observed at around 1 and 2.5 GPa, closely corresponding to critical electronic transitions, including bandgap closure and enhanced electron–phonon coupling. Anisotropic dielectric calculations further demonstrate that these transitions are primarily driven by dielectric property evolution along the armchair direction. This work paves the way for pressure-designed multifunctional engineering in van der Waals materials.