Evidence for chiral supercurrent in quantum Hall Josephson junctions.

Area of Science:

• Condensed Matter Physics
• Quantum Information Science
• Materials Science

Background:

• Hybridizing superconductivity with the quantum Hall (QH) effect offers potential for non-Abelian states in topological quantum computation.
• Experimental progress has been made, but direct evidence for chiral QH Josephson junctions, essential for superconducting QH circuits, remains elusive.
• The expected signature is a chiral supercurrent in QH edge channels with 2ϕ₀ magnetic flux periodicity.

Purpose of the Study:

• To provide concrete evidence for a chiral quantum Hall Josephson junction.
• To investigate the properties of supercurrents in graphene nanoribbons under quantum Hall conditions.
• To explore the feasibility of using these junctions for topological quantum computation.

Main Methods:

• Fabrication of ultra-narrow Josephson junctions in encapsulated graphene nanoribbons.
• Measurement of supercurrents in high magnetic fields (up to 8 T).
• Analysis of supercurrent oscillations and their dependence on junction geometry and magnetic flux.

Main Results:

• Observation of a chiral supercurrent in graphene nanoribbons at the quantum Hall plateau (resistance h/2e²).
• Reproducible 2ϕ₀-periodic oscillations of the supercurrent were observed.
• Reducing the superconductor/normal interface length was found to be crucial for measurable supercurrents on QH plateaus.

Conclusions:

• The study provides the first concrete evidence for a chiral quantum Hall Josephson junction.
• These findings validate theoretical predictions regarding dephasing at superconductor/normal interfaces.
• The results are significant for developing superconducting devices based on correlated and fractional QH effects for hosting non-Abelian Majorana and parafermion zero modes.