[Prof. Gil Young Cho] Robust Interlayer-Coherent Quantum Hall States i…

Caption: Phase diagram of twisted bilayer graphene with exciton condensates (Schematics)

Robust Interlayer-Coherent Quantum Hall States in Twisted Bilayer Graphene

We introduce a novel two-dimensional electronic system with ultrastrong interlayer 

interactions, namely twisted bilayer graphene with a large twist angle, as an ideal ground 

for realizing interlayer-coherent excitonic condensates. In these systems, subnanometer

atomic separation between the layers allows significant interlayer interactions, while

interlayer electron tunneling is geometrically suppressed due to the large twist angle. By 

fully exploiting these two features we demonstrate that a sequence of odd-integer 

quantum Hall states with interlayer coherence appears at the second Landau level (N = 1). 

Notably the energy gaps for these states are of order 1 K, which is several orders of

magnitude greater than those in GaAs. Furthermore, a variety of quantum Hall phase 

transitions are observed experimentally. All the experimental observations are largely 

consistent with our phenomenological model calculations. Hence, we establish that a large 

twist angle system is an excellent platform for high-temperature excitonic condensation.