Observation of a hole-side ν=7/2 fractional quantum Hall state in trilayer graphene

The intertwined many-body correlation, nontrivial topology, and symmetry can lead to exotic low-energy quasiparticle excitation, such as fractional quantum Hall (FQH) states, Fermi liquids, etc. Some FQH states with even denominators appearing at the half-filling of Landau levels (LLs) can be interpreted by Moore-Read theory, and the corresponding composite fermions satisfy non-Abelian statistics and have the potential to realize topological quantum computation. Possessing extraordinary tunability that stems from the intricate interplay of spin, valley, and orbital degrees of freedom, few-layer graphene stands out as an ideal platform for studying the FQH effect. Here we report the observation of the ν=7/2 FQH state on the hole side of Bernal-stacked trilayer graphene (B-TLG) unilaterally encapsulated with hexagonal boron nitride (hBN) - the first realization of this state on the hole side of pristine trilayer graphene. In contrast to recently reported electron-side even-denominator states hosted in the monolayer-like N=0 orbital, the ν=7/2 state emerges in the bilayer-like N_B=1 orbital near its crossing with the N_B=0 level, and exhibits a transport activation gap of Δ_tr=45.6±8.4 K, nearly two orders of magnitude larger than its electron-side counterparts. This value, obtained from Arrhenius analysis of the temperature-dependent residual resistance, is a conservative lower bound, as the analysis is limited by the residual-resistance floor. Our results suggest that few-layer graphene is an ideal platform for studying low-dimensional correlation states.