Researchers have made a significant breakthrough by observing fractional quantum Hall (FQH) physics at 1/3 total filling in balanced large angle twisted bilayer graphene. This discovery offers new insights about excitonic superfluid states and their underlying physics, marking an important step forward in the exploration of quantum materials.
The findings, published on July 22, 2025, reveal the unique properties of large angle twisted bilayer graphene (LATBG), which enables exceptionally strong interlayer Coulomb interactions. Unlike traditional semiconductor systems, where tunneling barriers pose challenges, LATBG operates under conditions where these obstacles are eliminated, allowing for unprecedented exploration of quantum phenomena.
“Here we report the observation of fractional quantum Hall physics at 1/3 total filling for balanced layer population in this system,” the researchers stated, underscoring the novelty of their results. The study demonstrated how these excitons, which consist of paired electrons and holes, achieve superfluid characteristics due to the strong interlayer interactions.
The research team, consisting of experts from institutions including DGIST and various universities, undertook extensive magnetotransport measurements alongside Monte Carlo simulations to analyze the emergent excitonic behaviors and their interactions. The experiments were conducted under high magnetic fields, up to 19 T, and at ultra-low temperatures of 30 mK, leading to the detection of clear conductivity minima characteristic of fractional quantum states.
“This state can be considered the fractional analog of the (111)-state occurring at total filling one due to the formation of excitons,” they explained, correlatively linking their findings to well-established concepts within quantum physics. Their work demonstrates how variations in displacement fields influence the system, leading to transitions between different FQH states and highlights the unique conditions under which these observations occur.
The exceptional characteristics of LATBG arise from the atomic-scale separation between layers, which facilitates strong Coulomb interactions without the interference usually encountered with tunneling barriers found in conventional bilayer systems. “Large angle twisted bilayer graphene is a powerful test bed for the exploration of correlation physics induced by interlayer Coulomb interactions of unprecedented strength,” the authors articulated, emphasizing the potential of this material for unlocking new physics.
Previous research on FQH states often struggled to demonstrate similar behaviors due to the limitations imposed by traditional semiconductor heterostructures. This recent study, through innovative use of advanced material systems and computational methods, successfully identifies ground states and transitions among fractional states with different topologies.
Detailed analyses of transport measurements revealed key insights; under certain balance conditions, where the charge carrier density among the two layers was equal, the FQH state emerged at the novel filling of 1/3. This finding contradicts expectations based solely on previous understandings of bilayer systems, where such states typically manifest at even numerator fractional fillings.
Overall, the research demonstrates the rich physics underlying this new phase of matter and sets the stage for increasingly sophisticated exploratory studies of twisted bilayer graphene systems. Researchers are optimistic about the ramifications of their findings, which may open new avenues for practical applications within quantum computing and advanced materials engineering.
“This work not only elucidates the nature of excitonic behaviors but also places large angle twisted bilayer graphene at the forefront of quantum research,” concluded the team. Future studies will likely focus on characterizing additional quantum states and exploring the full range of phenomena associated with this exciting material.