Superconducting state of the van der Waals layered PdH2 structure at high pressure

Abstract

We report structural and superconducting transitions in layered van der Waals (vdW) palladium dihydride (PdH2) calculated under high-pressure compression. PdH2 has a Hexagonal Closed-Packed (HCP) structure with a space group of P63mc, and has a superconducting transition temperature of 24 K at ambient pressure. At 15 GPa, the crystalline to vdW layered structural transition occurs, while the superconductivity remains. On compressing from 15 to 50 GPa, the Tc increased abnormally by 3.5 K. It is found that the superconducting critical temperature of P63mc PdH2 is determined by the out-of-plane interlayer breathing vibrational mode. As a vdW layered metal hydride superconductor, PdH2 provides a platform to study hydride superconductivity in such kinds of materials.