Double-dome superconductivity in germanium phosphides

Abstract

High pressure techniques have attracted massive attention in the investigation of the structural phase transitions and unexpected physical properties of layered 2D materials. Germanium phosphides possess a similar layered structure to black phosphorus (BP) and much better electronic transport capability in their enriched compositions. However, the detailed phase diagram for the Ge–P systems thus far remains incomplete. In this work, by the use of the particle swarm optimization method and first-principles calculations, we have identified a series of pressure-induced novel structures in phosphorous-rich germanides with various Ge and P atomic ratios ranging from 1 : 1 to 1 : 5, in which phonon-mediated superconductors are revealed. Our calculations demonstrate that the superconductors exhibit an unusual M-shaped double dome character. In the low-pressure dome, a strong electron–phonon coupling (λ ∼ 1.0) attributed to the softened phonon modes appears especially in the metallic phase of GeP within the NaCl structure, showing a T_c of 18 K at 8 GPa, whereas the high-pressure superconductivity dome is related to the peculiar band structure and the compensation of different behaviors of λ and ω_log, leading to a T_c ∼ 20 K in GeP₄ at 120 GPa, which is the highest value thus far reported in BP-based materials. The unusual finding of double dome superconductivity in Ge–P compounds can pave the way for the physical understanding of pressure-derived superconductors.