Probing Excitonic Superfluid Correlations in Bilayer Graphene Using Gate-Defined Weak-Link Device

Graphene double layers separated by a thin insulating spacer provide a versatile setting to explore collective phases of interlayer excitons. When each layer is tuned to half filling in the lowest Landau level, excitonic condensation leads to a superfluid ground state. While this state shares certain features with superconductors, a direct analogue of the Josephson effect has not yet been observed in excitonic superfluid. To address this challenge, we have developed a new device geometry that introduces a controllable weak link into the excitonic system. The device consists of a narrow slit patterned in the top gate, with an additional metal gate used to tune the carrier density of the slit region. This architecture is designed to probe phase coherence and transport across the constriction, providing a pathway to test for Josephson Junction-like phenomena and to study excitonic correlations in a new regime. We will show our results at the presentation.