Superconductivity in Empty Bands and Multiple Order Parameter Chirality.

Area of Science:

• Condensed Matter Physics
• Quantum Materials
• Superconductivity

Background:

• Experiments show light polarization rotation upon reflection from superconductors.
• Photon energy exceeding electronic bandwidth suggests roles for filled or empty bands.

Purpose of the Study:

• To explain the observed light polarization rotation in superconductors.
• To investigate the role of Coulomb interactions and order parameters in unoccupied bands.

Main Methods:

• Utilizing strong-coupling theory to model Coulomb interactions.
• Analyzing the implications of experimental observations on the order parameter's form.

Main Results:

• A Coulomb interaction can generate an order parameter in unoccupied bands, explaining experimental results.
• The study proposes the first detection of a superconducting order parameter in a band far from the Fermi energy.
• A positive Kerr effect indicates broken time reversal and mirror symmetries in the ordered phase.

Conclusions:

• The findings provide tight constraints on the order parameter's form across different bands.
• Experiments may have detected a superconducting order parameter in a previously inaccessible band.
• Analysis suggests different order parameter chiralities in UPt3, hinting at complex topological superconductivity.