Superconductivity mediated by charge fluctuations in layered molecular crystals

Area of Science:

• Condensed Matter Physics
• Materials Science
• Quantum Chemistry

Background:

• Layered molecular crystals exhibit complex phase competition between superconductivity, charge order, and metallic states.
• The theta and beta(") crystal structures are key to understanding these competing electronic phases.
• Distinguishing between different mechanisms of superconductivity is crucial for materials design.

Purpose of the Study:

• To investigate the microscopic mechanisms driving superconductivity in theta and beta(") layered molecular crystals.
• To compare the superconductivity mechanism with that found in the kappa-(BEDT-TTF)(2)X family.
• To identify materials likely to exhibit superconductivity under applied pressure.

Main Methods:

• Application of slave-boson theory to the extended Hubbard model.
• Theoretical analysis of charge and spin fluctuations.
• Symmetry analysis of Cooper pairs.

Main Results:

• Superconductivity in theta and beta(") structures is mediated by charge fluctuations.
• Cooper pairs in these systems possess d(xy) symmetry.
• This contrasts with kappa-(BEDT-TTF)(2)X, where superconductivity is mediated by spin fluctuations with d(x(2)-y(2)) symmetry.

Conclusions:

• Charge fluctuations are a viable mechanism for superconductivity in specific layered molecular crystals.
• The d(xy) symmetry of Cooper pairs offers a distinct signature compared to other related materials.
• Pressure is predicted to induce superconductivity in several candidate materials.