Resistivity of high pressure phosphorus phases

Simple cubic (sc) black phosphorus (denoted BP), stable at P>10GPa, seems an ordinary metal. It has electron-phonon-driven superconductivity with Tc 5-10 K. The A17 phase, stable at atmospheric pressure, has a narrow gap, becomes semimetallic at P=1 GPa, and has a smooth transition to topological metal behavior at P ~ 5 GPa. The A7 phase, stable for 5<P<10 GPa, is metallic, superconducting, and less conventional than the sc phase. Some insights are extracted from analysis of resistivity versus temperature at various pressures. A surprising order-of-magnitude disagreement between theory and experiment is discussed.