Manipulating fractional Shapiro steps in twisted cuprate Josephson junctions

Area of Science:

• Condensed Matter Physics
• Superconductivity
• Materials Science

Background:

• Twisted cuprate superconductors offer potential for high-temperature superconducting devices.
• The presence of high-temperature topological superconductivity in these materials is an unresolved question.

Purpose of the Study:

• To investigate the occurrence and stability of half-integer Shapiro steps in twisted cuprate Josephson junctions.
• To explore the relationship between these steps and topological superconductivity.
• To understand the tunability of the current-phase relation (CPR).

Main Methods:

• Fabrication of Josephson junctions using twisted cuprate superconductors.
• Measurement of Shapiro steps at specific twist angles (e.g., 45°).
• Thermal cycling and application of magnetic fields or electrical currents for sample training and annealing.

Main Results:

• Half-integer Shapiro steps were observed at a 45° twist angle but were unstable under thermal cycling.
• Fractional steps, including those with odd denominators, were achievable through sample training and current annealing, indicating a tunable CPR.
• Half-integer steps were induced outside the expected topological superconductivity regime, suggesting a vortex-related mechanism.

Conclusions:

• The direct association of half-integer Shapiro steps with topological superconductivity in twisted cuprates should be approached with caution.
• An alternative mechanism, potentially involving trapped vortices, may explain the observed phenomena.
• The study opens avenues for developing Josephson junctions with electrically tunable CPRs at high temperatures.