Optimized unconventional superconductivity in a molecular Jahn-Teller metal

Area of Science:

• Condensed Matter Physics
• Materials Science
• Quantum Chemistry

Background:

• Unconventional superconductors present a challenge in understanding the interplay between superconducting, insulating, and metallic states.
• Molecular fulleride superconductors share similarities with cuprates, featuring an antiferromagnetic insulator.
• The unique electronic structure of C60 (3-) anions and the Jahn-Teller effect are key in fullerides.

Purpose of the Study:

• To elucidate the relationship between the insulating, metallic, and superconducting states in molecular fulleride superconductors.
• To identify the electronic state responsible for bridging the insulating and superconducting phases.
• To investigate the role of molecular electronic structure and lattice parameters in controlling superconductivity.

Main Methods:

• Theoretical analysis of electronic structure.
• Identification of the Jahn-Teller metal as a key intermediate state.
• Correlation of superconducting transition temperature (Tc) with interfulleride separation.

Main Results:

• The Jahn-Teller metal state is characterized by a fluctuating, microscopically heterogeneous coexistence of localized Jahn-Teller-active and itinerant electrons.
• This state acts as a bridge connecting the insulating and superconducting phases in fullerides.
• Superconducting transition temperature (Tc) exhibits a dome-shaped dependence on the interfulleride separation.

Conclusions:

• Molecular electronic structure, specifically via the Jahn-Teller effect, directly controls superconductivity in fullerides.
• The Jahn-Teller metal provides a unified framework for understanding the diverse electronic states in these materials.
• Understanding these molecular and lattice electronic features is crucial for designing new superconductors.