Helical Edge States and Quantum Phase Transitions in Tetralayer Graphene

Abstract

Helical conductors with spin-momentum locking are promising platforms for Majorana fermions. Here we report observation of two topologically distinct phases supporting helical edge states in charge neutral Bernal-stacked tetralayer graphene in Hall bar and Corbino geometries. As the magnetic field B and out-of-plane displacement field D are varied, we observe a phase diagram consisting of an insulating phase and two metallic phases, with 0, 1 and 2 helical edge states, respectively. These phases are accounted for by a theoretical model that relates their conductance to spin-polarization plateaus. Transitions between them arise from a competition among inter-layer hopping, electrostatic and exchange interaction energies. Our work highlights the complex competing symmetries and the rich quantum phases in few-layer graphene.

Accepted by PRL

References in corpus (14)

• Quantum Spin Hall Insulator State in HgTe Quantum Wells
• Signatures of Majorana fermions in hybrid superconductor-semiconductor nanowire devices
• Majorana Fermions and a Topological Phase Transition in Semiconductor-Superconductor Heterostructures
• The zero-energy state in graphene in a high magnetic field
• Edge States and the Quantized Hall Effect in Graphene
• Evidence for a Spin Phase Transition at ν=0 in Bilayer Graphene
• Charge and Spin Transport at the Quantum Hall Edge of Graphene
• Edge excitations of the canted antiferromagnetic phase of the $\nu =0$ quantum Hall state in graphene: a simplified analysis
• Insulating state in tetralayers reveals an even-odd interaction effect in multilayer graphene
• Tunable symmetries of integer and fractional quantum Hall phases in heterostructures with multiple Dirac bands
• Metallic Phase and Temperature Dependence of the $\nu =0$ Quantum Hall State in Bilayer Graphene
• Collective Edge Modes near the onset of a graphene quantum spin Hall state
• Spin-Valley Coherent Phases of the $\nu =0$ Quantum Hall State in Bilayer Graphene
• Valley-kink in Bilayer Graphene at $\nu =0$: A Charge Density Signature for Quantum Hall Ferromagnetism