Even-Denominator Fractional Quantum Hall States in the Zeroth Landau Level of the Monolayer-like Band of ABA Trilayer Graphene

Abstract

Even-denominator fractional quantum Hall states (FQHSs) at half-filling are particularly intriguing due to their predicted non-Abelian excitations with non-trivial braiding statistics. Conventional theory suggests that such states primarily emerge in the first excited Landau level, a notion supported by existing experimental evidence. In this research article, we present an unexpected discovery of plausibly non-Abelian even-denominator FQHSs in the zeroth Landau level of Bernal-stacked trilayer graphene. Specifically, we observe robust FQHSs at filling factors ν = 5/2 and ν = 7/2, accompanied by their theoretically predicted Levin-Halperin daughter states at ν = 9/17 and ν = 7/13, respectively. Additionally, further away from these states, the standard Jain sequence of composite fermions (CFs) is detected. The even-denominator FQHSs and their corresponding daughter states strengthen with increasing magnetic fields, while the CF states weaken simultaneously. Interestingly, these even-denominator (and their daughter) FQHSs only appear at a finite displacement field, precisely when two Landau levels - originating from a monolayer-like band of trilayer graphene with distinct isospin indices - cross each other. We propose that the system’s lack of inversion symmetry leads to additional isospin interactions, enhancing Landau level mixing between these intersecting states and softening the short-range component of Coulomb repulsion, thereby stabilizing the even-denominator FQHSs. Our study challenges the current theoretical framework of even-denominator fractional quantum Hall states and expands the range of systems where they can be explored. It positions multilayer graphene as a promising platform for hosting Majorana excitations, potentially advancing fault-tolerant topological quantum computing.