Ferroelectric and anomalous quantum Hall states in bare rhombohedral trilayer graphene

TL;DR

This study provides transport evidence for multiple spontaneous quantum Hall states and ferroelectric phases in rhombohedral trilayer graphene, revealing complex electron interactions and phase coexistence in a simple material.

Contribution

It experimentally confirms four of five predicted quantum Hall phases and uncovers ferroelectric behavior in zeroth Landau level ferromagnets.

Findings

Observation of quantum Hall states with Chern numbers 3 and 6.

Identification of ferroelectricity with spontaneous layer polarization.

Detection of magnetic and electric hysteresis in the states.

Abstract

Nontrivial interacting phases can emerge in elementary materials. As a prime example, continuing advances in device quality have facilitated the observation of a variety of spontaneous quantum Hall-like states, a cascade of Stoner-like magnets, and an unconventional superconductor in bilayer graphene. Its natural extension, rhombohedral trilayer graphene is predicted to be even more susceptible to interactions given its even flatter low-energy bands and larger winding number. Theoretically, five spontaneous quantum Hall phases have been proposed to be candidate ground states. Here, we provide transport evidence for observing four of the five competing ordered states in interaction-maximized, dually-gated, rhombohedral trilayer graphene. In particular, at vanishing but finite magnetic fields, two states with Chern numbers 3 and 6 can be stabilized at elevated and low electric fields, respectively, and both exhibit clear magnetic hysteresis. We also reveal that the quantum Hall ferromagnets of the zeroth Landau level are ferroelectrics with spontaneous layer polarizations even at zero electric field, as evidenced by electric hysteresis. Our findings exemplify the possible birth of rich interacting electron physics in a simple elementary material.