Experimental detection of vortices in magic-angle graphene

Area of Science:

• Condensed Matter Physics
• Materials Science
• Superconductivity

Background:

• Magic-angle twisted-layer graphene (MATLG) shows tunable superconductivity, but its phenomenology is underexplored.
• Studying 2D materials presents unique experimental challenges.
• Superconducting vortices are characteristic of type-II superconductors.

Purpose of the Study:

• To provide direct experimental evidence of superconducting vortices in MATLG.
• To characterize vortex dynamics in 2D superconducting systems.
• To establish gate-defined Josephson junctions as tools for studying 2D superconductors.

Main Methods:

• Fabrication of gate-tuned Josephson junctions in MATLG.
• Field-dependent critical current measurements.
• Time-dependent measurements of voltage-current (V-I) fluctuations.

Main Results:

• Observed Fraunhofer-like patterns in critical current, indicating weak transverse screening.
• Detected spontaneous vortex penetration into leads, causing pattern shifts.
• Measured vortex energy scale, London penetration depth, and superfluid stiffness via V-I fluctuations.

Conclusions:

• First direct evidence of superconducting vortices in MATLG.
• Gate-defined Josephson junctions are effective for probing vortex dynamics in 2D superconductors.
• Findings advance understanding of superconductivity in novel 2D materials.