Pressure-Driven Dimensional Modulation of Phase Transitions and Superconductivity in Black Phosphorus.

Thickness and pressure cooperatively modulate the transport properties in layered materials─particularly two-dimensional (2D) superconductivity─which are intrinsically governed by quantum confinement and anisotropic interactions. Here, through systematic investigation of thickness-dependent pressure-induced phenomena in black phosphorus, we reveal the mechanism by which dimensional confinement governs metallization and superconductivity via modulation of the electronic structure. Robust 2D superconductivity, observed in both few-layer samples and nanoflakes within the bulk, underscores quantum confinement as the fundamental origin of 2D superconductivity. Furthermore, the 3D-2D crossover in bulk highlights the critical role of weak interlayer coupling in stabilizing 2D superconducting behavior. Remarkably, quantum confinement dramatically enhances the critical field, with the in-plane critical field in 6-layer sample exceeding the Pauli limit due to enhanced spin-orbit scattering. These findings provide new insights into engineering superconducting dimensionality and properties via combined thickness and pressure control.