Emerging Interlayer Coherence in Twist-Controlled Graphene Double Layers*

In closely spaced double layer systems in the quantum Hall regime, enhanced interlayer interactions can lead to interlayer exciton condensates when each layer is at half-integer filling of the lowest Landau level. We study interlayer tunneling in double layers of graphene separated by a thin hBN tunnel barrier, where accurate rotational alignment of the graphene monolayers leads to energy and momentum conserving resonant tunneling. At half-integer layer fillings of the lowest orbital Landau level, we observe Josephson-like zero-bias tunneling conductance peaks that are insensitive to variations of layer filling factors. The zero-bias tunneling conductance peaks have a significantly narrower linewidth compared to 2D-2D tunneling resonances observed at zero magnetic field when the energy bands of the two layers are aligned, indicating that electrons occupy an interlayer coherent superposition of states in both layers. Additionally, the tunneling spectrum provides insight into the types of paired states. Our results establish twist control as key to probing interlayer exciton condensates through tunneling anomalies in double layers of two-dimensional materials.