Universal chiral Luttinger liquid behavior in a graphene quantum point contact

The chiral Luttinger liquid theory of fractional quantum Hall (FQH) edges predicts a soft-gap in the tunneling density of states at the Fermi energy whose scaling exponent “g” is determined by the topological order of the enclosed bulk [1]. For a Laughlin-like state with a single edge mode, the exponent g = 1/ν is not expected to be renormalized in the presence of intra-edge electron-electron interactions. This prediction has not been confirmed experimentally, and previous tunneling measurements have found that the value of “g” does depend on the nature of the tunnel barrier [2], possibly due to edge reconstruction effects. To remedy this issue, we employ a dual-graphite gated, hBN encapsulated, monolayer graphene quantum point heterojunction which presents an ultra-clean platform which can be tuned to directly couple ν = 1/3 and a ν = 1 edge modes at a single point. In the first of two talks, we will discuss our measurements of the tunneling conductance across the junction and observation of a power law dependence in voltage bias and temperature, which are both found to be quantitatively consistent with the prediction of the chiral Luttinger liquid theory for a ν = 1/3 edge. Additionally, the temperature-scaled tunneling conductance collapses onto the predicted universal curve, providing the best confirmation to date of the chiral Luttinger liquid theory of FQH edge modes.

[1] Wen, X. G., 1990, Phys. Rev. B 41, 12 838–12 844

[2] Chang, et.al., 1996, Phys. Rev. Lett. 77, 2538– 2541