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Flatbands, Landau levels, Hall conductivity and Hofstadter butterfly in large-angle twisted bilayer graphene: a high pressure study

Ayan Mondal,Priyanka Sinha,B. Chittari

Published 2025 in Journal of Physics: Condensed Matter

ABSTRACT

Twisted bilayer graphene (TBG) hosts strongly correlated phases at the magic angle ( ∼1.1∘), but these effects are suppressed at larger, more experimentally accessible twist angles where the electronic bands are typically dispersive. We demonstrate that perpendicular pressure can restore this flatband physics in large-angle TBG by systematically enhancing interlayer coupling. These pressure-induced flatbands exhibit strong electronic localization in AA-stacked regions, mimicking the magic-angle case. In a magnetic field, these flatbands give rise to an integer quantum Hall effect with a characteristic zero-energy plateau. At higher twist angles, this behavior evolves, and additional asymmetric plateaus emerge due to broken particle-hole symmetry. This topological correspondence is confirmed by the Hofstadter butterfly spectrum, which reveals the requisite low-energy gaps that align with the Hall conductivity plateaus. Our results establish a fundamental limit to this effect: while pressure extends magic-angle behavior to moderate twists, moiré correlations weaken beyond a critical angle of ∼6∘. Ultimately, our work establishes pressure as a powerful tuning knob to engineer correlated and topological phases in moiré systems, offering an experimentally robust alternative to precise twist-angle control.

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