Exploring phonon mediated superconductivity of and under high pressure insight from first-principles calculations

Abstract

Investigating novel materials under high pressure presents a challenge in condensed matter physics. In this study, we examine and, materials identified through an evolutionary algorithm, which exhibit thermodynamic stability up to at least 100 GPa. Our findings reveal that exhibits a rhombohedral structure () at pressures ranging from 0 GPa to 25 GPa, transitioning to a hexagonal structure () between 50 GPa and 100 GPa. In contrast, is predicted to have a monoclinic structure (C2/m) at low pressures and a hexagonal structure () at higher pressures. Notably, both materials are dynamically stable within the harmonic approximation at pressures beyond 15 GPa for and beyond 25 GPa for. Furthermore, accurately capturing the thermal lattice vibrations of these materials under strong quantum anharmonicity requires advanced methods. Using a stochastic approach to self-consistent harmonic approximation (SSCHA), we introduce anharmonic corrections to further explore lattice dynamics. For superconducting properties, shows a remarkable critical temperature () of 44.5 K at a pressure of 25 GPa, as predicted within the harmonic approximation. In comparison, achieves a of approximately 13 K at a pressure of 50 GPa when anharmonic corrections are applied using the Allen-Dynes modified McMillan equation. Our findings bridge a gap in understanding electronic band structure, phonon linewidth impacts, and vibrational modes under pressure, offering key insights into phase stability and superconducting mechanisms. These findings introduce a promising new class of materials, emphasizing their potential to enrich superconductivity research by advancing previously overlooked substances.