We present a detailed experimental study of the effect of Landau level mixing on various fractional quantum Hall states (FQHs) about half filling in a multiband system, namely, Bernal stacked trilayer graphene (TLG). In pristine TLG, the excitation energy gaps, Landé $g$ factor, effective mass, and disorder broadening of the odd-denominator FQHs are identical to their hole-conjugate counterpart. This precise particle-hole symmetry (PHS) stems from the lattice mirror symmetry that precludes Landau level mixing. Introducing a nonzero displacement field $D$ disrupts this mirror symmetry, facilitating the hybridization between the monolayerlike and bilayerlike Landau levels. This interband coupling enhances the Landau level mixing factor $\eta$ and activates three-body interactions—both of which explicitly break the PHS of FQHs. As a result, various conventional FQHs are completely destabilized, offering a route to explore such mixing effects on FQHs in a controlled way. We establish that the PHS breaking in TLG is of extrinsic origin and is fundamentally distinct from the intrinsic, interaction-driven symmetry breaking observed in the lowest Landau levels of single-layer and bilayer graphene.

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• Fractional quantum Hall effect
• Landau levels
• Graphene
• Strongly correlated systems