Emergent superconductivity in K2ReH9 under pressure

Abstract

Pressure, as a controllable thermodynamic parameter, can substantially modulate the structural topologies, e.g., phase transition, and electronic properties of the known compounds. Herein, we found that the compression of H-rich compounds, stabilizing at ambient conditions, is an applicable route to achieve high-temperature superconductivity at a lower pressure (<100 GPa). First-principles calculations reveal that under compression, K₂ReH₉ experiences structural transforms from P2m symmetry to Pmma phase via an intermediate Pma2 phase, then to P6₃/mcm phase, accompanied by semiconductor-to-metal transition. More interestingly, the estimated superconducting transition temperature (T_c) of P6₃/mcm phase is up to 127.1 K at 75 GPa, comparable to the well-known LaBH₈, a low-pressure dynamically stable superconductor. Additionally, from Pmma to P6₃/mcm phase, the enhanced number of H–H covalent bonds and their weakened strength, caused by the rotation of H triangles in ReH₁₂ icosahedra, are responsible for the remarkable elevation of T_c value.