Metastable π junction between an s(±)-wave and an s-wave superconductor

Area of Science:

• Condensed matter physics
• Superconductivity
• Materials science

Background:

• Superconductors with sign-changing order parameters exhibit unique electronic properties.
• Josephson junctions are crucial for understanding superconducting device behavior.
• Experimental observations of half-integer flux quantum transitions in composite superconductors present a puzzle.

Purpose of the Study:

• To investigate the interfacial effects between a sign-changing superconductor and a conventional superconductor.
• To explore the theoretical implications of Josephson coupling frustration at such interfaces.
• To provide a potential explanation for observed half-integer flux quantum phenomena.

Main Methods:

• Utilizing a Ginzburg-Landau-type theoretical model.
• Analyzing the Josephson coupling across the interface considering different Fermi surface portions.
• Investigating energy-phase relations and symmetry properties at the interface.

Main Results:

• Demonstrated that frustration of Josephson coupling can lead to time-reversal symmetry breaking at the interface.
• Identified unusual energy-phase relations with multiple local minima.
• The model predicts phenomena consistent with experimental findings in niobium-iron pnictide superconducting loops.

Conclusions:

• The interface between unconventional and conventional superconductors can host novel phenomena.
• Time-reversal symmetry breaking and complex energy landscapes are key consequences.
• This theoretical framework offers a plausible explanation for half-integer flux quantum transitions.