Helical Edge States and Quantum Phase Transitions in Tetralayer Graphene.,Physical Review Letters

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Helical Edge States and Quantum Phase Transitions in Tetralayer Graphene.
Physical Review Letters ( IF 8.1 ) Pub Date : 2020-07-13 , DOI: 10.1103/physrevlett.125.036803
Shi Che ₁ , Yanmeng Shi ₂ , Jiawei Yang ₁ , Haidong Tian ₁ , Ruoyu Chen ₁ , Takashi Taniguchi ₃ , Kenji Watanabe ₃ , Dmitry Smirnov ₄ , Chun Ning Lau ₁ , Efrat Shimshoni ₅ , Ganpathy Murthy ₆ , Herbert A Fertig ₇

Affiliation

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 interlayer hopping, electrostatic and exchange interaction energies. Our work highlights the complex competing symmetries and the rich quantum phases in few-layer graphene.

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