Quantum Parity Hall effect in ABA Graphene

TL;DR

This paper reports a new quantum Hall effect in ABA-stacked graphene trilayers, where boundary channels are distinguished by parity, showing quantized conductance changes driven by magnetic field and interactions, revealing a topological phase protected by symmetry.

Contribution

The study introduces the quantum parity Hall effect in ABA graphene trilayers, highlighting parity-based boundary states and their tunable topological phase transitions driven by magnetic field and Coulomb interactions.

Findings

Quantized conductance of 4e^2/h at charge neutrality

Transition to 2e^2/h indicating spin-polarized edge states

Further decrease to approximately 0 conductance with increasing magnetic field

Abstract

The celebrated phenomenon of quantum Hall effect has recently been generalized from transport of conserved charges to that of other approximately conserved state variables, including spin and valley, which are characterized by spin- or valley-polarized boundary states with different chiralities. Here, we report a new class of quantum Hall effect in ABA-stacked graphene trilayers (TLG), the quantum parity Hall (QPH) effect, in which boundary channels are distinguished by even or odd parity under the systems mirror reflection symmetry. At the charge neutrality point and a small perpendicular magnetic field $B_{\perp}$, the longitudinal conductance $\sigma_{xx}$ is first quantized to $4e^2/h$, establishing the presence of four edge channels. As $B_{\perp}$ increases, $\sigma_{xx}$ first decreases to $2e^2/h$, indicating spin-polarized counter-propagating edge states, and then to approximately $0$. These behaviors arise from level crossings between even and odd parity bulk Landau levels, driven by exchange interactions with the underlying Fermi sea, which favor an ordinary insulator ground state in the strong $B_{\perp}$ limit, and a spin-polarized state at intermediate fields. The transitions between spin-polarized and unpolarized states can be tuned by varying Zeeman energy. Our findings demonstrate a topological phase that is protected by a gate-controllable symmetry and sensitive to Coulomb interactions.