Emergent partons in fractional quantum Hall systems

In the fractional quantum Hall effect, electrons can fractionalize into quasiparticles. These are referred to as partons, and this picture provides an intuitive framework for understanding fractionalized states. Low-energy partons are equivalent to the established composite fermion states. High-energy partons are predicted to exist, but have not yet been demonstrated experimentally. Recently, a geometrical theory for the fractional quantum Hall effect was proposed. In this description, chiral spin-2 neutral excitations—also termed gravitons—arise from fluctuations of the quantum metric. Here we report the observation of multiple chiral gravitons using circularly polarized resonant inelastic light scattering. At a filling factor of 2/7, our experiments reveal two sharp modes with opposite chiralities that we identify as low- and high-energy gravitons. By contrast, at a filling factor of 2/9, multiple gravitons exhibit the same chirality. In the gapless Fermi-liquid-like state at a filling factor of 1/4, the high-energy graviton persists as a gapped chiral excitation. These observations identify chiral gravitons as geometrical excitations of their corresponding partons. Our work introduces a method to detect partons through chiral graviton measurements, opening the exploration of fractionalized matter. In a geometrical theory for the fractional quantum Hall effect, chiral spin-2 neutral excitations arise. Now, multiple such excitations are observed and provide evidence for the parton description of the quantum Hall effect.