Superconductivity and strong anharmonicity in novel Nb-S phases

Area of Science:

• Materials Science
• Condensed Matter Physics
• Computational Chemistry

Background:

• Understanding the phase diagram of binary systems like Niobium-Sulfur (Nb-S) is crucial for discovering new materials with unique properties.
• High-pressure research often reveals novel phases and phenomena not observed at ambient conditions.

Purpose of the Study:

• To computationally explore the Nb-S phase diagram across a wide pressure range (ambient to 250 GPa).
• To predict new stable Nb-S compositions and phases.
• To investigate the electronic, vibrational, and superconducting properties of these phases, including the impact of anharmonicity.

Main Methods:

• Utilizing *ab initio* evolutionary crystal structure prediction to explore the phase space.
• Performing electronic structure calculations to determine material properties.
• Investigating phonon dynamics and electron-phonon (ep) coupling strengths.
• Analyzing the effects of phonon anharmonicity on lattice stability and superconductivity.

Main Results:

• Several new stable Nb-S compositions and phases were identified, particularly at high pressures.
• All predicted stable phases, except for low-pressure sulfur, are metallic.
• Electron-phonon coupling strengths are generally low, leading to critical superconducting temperatures below 15 K.
• Phonon anharmonicity was found to stabilize the novel high-pressure phase of Nb2S and enhance its ep interaction.

Conclusions:

• The Nb-S system exhibits complex phase behavior under high pressure, with the emergence of new metallic phases.
• While intrinsic superconductivity in these phases is limited, the study highlights the significant role of phonon anharmonicity in modulating material properties.
• This work provides a theoretical foundation for future experimental investigations of Nb-S under extreme conditions.