Pressure-driven superconductivity in layered isostructural germanium phosphides

The discovery of superconductivity and its modulation are long-standing cutting-edge research topics in condensed matter physics. As a powerful tool, the high-pressure technique can be used to achieve novel superconductors and tune their physical properties. One typical example is binary germanium phosphides with different stoichiometries, which exhibit abundant physical properties with layered lattice structures similar to blue phosphorus. The detailed phase diagrams of the Ge–P systems are important for understanding the influence of stoichiometry on pressure-driven superconductivity, but it remains unexplored. Here, we measured and compared the detailed superconducting phase diagrams of the Ge–P systems of layered isostructural germanium phosphides GeP3 and GeP5 under pressure. Even though these two binary phosphides exhibit obviously different atomic occupations in the crystal structure due to their distinct stoichiometric ratios, the onset superconducting transition temperatures Tc of GeP3 and GeP5 both show dramatic enhancements from ∼2.5 K at 12.0 GPa to the maximum values of ∼9.0 K at 28.0 GPa, which are higher than those of other binary metal phosphides. Such pressure-enhanced superconductivity therein is accompanied by significant pressure-induced phonon mode softening, which is confirmed via in situ high-pressure Raman measurements. Our observations deepen the physical understanding of pressure-driven superconductivity in phosphorous-rich layered compounds and pave the way for potential applications in microsuperconducting devices.