Manipulating ambient pressure superconductivity in metal borocarbides through hole doping

Area of Science:

• Materials Science
• Condensed Matter Physics
• Computational Materials Science

Background:

• Machine learning (ML) guided structure search identified a metastable Ca2B4C4 compound with low formation energy but poor superconducting properties.
• Understanding factors influencing superconductivity in novel compounds is crucial for discovering high-temperature superconductors.

Purpose of the Study:

• To explore the potential of boron-carbon (B-C) compounds as high-temperature superconductors.
• To investigate the effect of hole doping on the superconducting properties of Ca-B-C systems.
• To identify key electronic structure features responsible for enhanced superconductivity.

Main Methods:

• Utilized machine learning (ML) for guided structure search to discover new materials.
• Employed density functional theory (DFT) calculations to predict material properties, including formation energy and superconducting transition temperature (Tc).
• Investigated electronic structure, focusing on electronic density of states (DOS) at the Fermi level and band structures.

Main Results:

• A Na-substituted Ca-B-C compound exhibited a significantly enhanced predicted superconducting transition temperature (Tc) of 21.9 K.
• Na substitution transformed Ca2B4C8 from a semiconductor to a superconductor with a Tc of 28.9 K.
• Identified flat sigma bands and a Van Hove singularity at the Fermi level as critical for enhanced superconductivity.

Conclusions:

• Introduced a new class of B-C-based superconductors with tunable properties.
• Demonstrated the effectiveness of hole doping (Na substitution) in enhancing superconductivity in these materials.
• Broadened the compositional space for the discovery of high-temperature superconducting materials.