Yuval Ronen Lab

The effective interaction between composite fermions, set entirely by the Coulomb potential and the underlying electronic Landau level orbitals, can stabilize exotic fractional quantum Hall states. In particular, half-filled Landau levels with different orbital character can host either metallic or paired phases of composite fermions. Here, we leverage experimental control over the orbital composition to realize a composite-fermion pairing transition in the first excited Landau level of bilayer graphene. Transport measurements at filling factors v = 9/2 and 11/2 reveal conductive states giving way to well-developed plateaus with increasing displacement fields. These states are insensitive to an in-plane magnetic field, indicating single-component ground states and thus pointing at non-Abelian orders. Our numerical study, based on displacement-field-dependent Landau-level wavefunctions, supports the orbital origin of the pairing transition and suggests Moore-Read or anti-Pfaffian ground states.

Twisted trilayer graphene (TTG) provides a tunable moiré platform to study correlated phases emerging from flat-band physics. Here, we investigate the interplay between superconductivity and spontaneous orbital magnetism (OM) in alternating TTG devices with intermediate twist angles (1.381.44°). Using electrostatically defined Josephson junctions, we demonstrate that OM, stabilized near the charge neutrality point (CNP), competes with gate-induced superconductivity. The OM phase is characterized by sharp jumps in Hall resistance, current-induced bistability, and a CurieBloch temperature dependence, indicating broken time-reversal symmetry. Additionally, nonreciprocal Josephson transport─manifested as asymmetric Fraunhofer patterns and a superconducting diode effect─provides independent evidence of an orbital magnetic state confined to the weak link. The observed critical temperature hierarchy, where superconductivity dominates over OM at higher carrier densities and displacement fields, reveals a tunable competition between two broken-symmetry ground states. Our findings establish alternating TTG Josephson devices as a minimal and versatile platform to probe the coexistence of magnetism and superconductivity in engineered moiré systems.

Even-denominator fractional quantum Hall states are promising candidates for fault-tolerant quantum computing due to their underlying non-Abelian topological order. However, the topological order of these states remains hotly debated. Here, we report transport measurements on ultra-clean bilayer graphene heterostructures, where we observed four quarter-filled states and their corresponding Levin-Halperin daughter states, constraining their topological order. Moreover, we complete the sequence of half-filled plateaus by detecting states at ν=−32 and ν=12 whose daughters suggest an alternating sequence of non-Abelian orders. This pattern suggests a universal origin supporting their use in identifying topological order at even-denominator fillings, though further confirmation is needed via direct measurements. The observed quarter- and half-filled states appear in N = 0 and N = 1 Landau levels, respectively, and thus highlight a competition between interactions favoring paired states of either four- or two-flux composite fermions. Additionally, we observe several next-generation quantum Hall states that require strong interactions between composite fermions.