Superconductivity Governed by Janus-Faced Fermiology in Strained Bilayer Nickelates.

Area of Science:

• Condensed Matter Physics
• Materials Science

Background:

• High-temperature superconductivity in bilayer nickelates (La,Pr)3Ni2O7 is a significant area of research.
• The fermiology, particularly the role of the $\gamma$ pocket, remains a key unresolved issue with conflicting experimental and theoretical results.

Purpose of the Study:

• To investigate the fermiology underlying superconductivity in pressurized and strained bilayer nickelates.
• To elucidate the role of the $\gamma$ pocket in spin-fluctuation-mediated superconductivity.

Main Methods:

• Theoretical investigation of the $\gamma$ pocket's influence on superconductivity.
• Analysis of spin-fluctuation-mediated pairing mechanisms.

Main Results:

• The $\gamma$ pocket exhibits a Janus-faced role, inducing both dominant pair-breaking and pair-forming channels for s±-wave pairing.
• Optimal superconducting transition temperature (Tc) is achieved when the $\gamma$ pocket surfaces at the Fermi level, near a Lifshitz transition.
• Superconductivity emerges when the $\gamma$ pocket's energy level is close to the Fermi level, either from below or above.

Conclusions:

• The study reconciles opposing viewpoints on the fermiology of nickelate superconductors.
• Findings explain recent experimental observations in (La,Pr)3Ni2O7 thin films, including strain effects and the dome shape of Tc.