posted on 2022-12-16, 15:41authored byDohun Kim, Byungmin Kang, Yong-Bin Choi, Kenji Watanabe, Takashi Taniguchi, Gil-Ho Lee, Gil Young Cho, Youngwook Kim
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, sub-nanometer 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.