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-1 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.
|Journal||Physical Review Letters|
|State||Published - Jul 17 2020|
Bibliographical noteFunding Information:
The experiments are supported by DOE BES Division under Grant No. DE- SC0020187. Device fabrication is partially supported by the Center for Emergent Materials: an NSF MRSEC under Grant No. DMR-1420451. Theoretical work was supported by the US-Israel Binational Science Foundation (Grant No. 2016130: G. M., H. A. F., E. S.; Grant No. 2018726: H. A. F., E. S.), by the NSF (Grant Nos. DMR-1506263, DMR-1914451, and ECCS-193640), and by the Israel Science Foundation (ISF) Grants No. 231/14 and 993/19 (E. S.). H. A. F. acknowledges the support of the Research Corporation for Science Advancement through a Cottrell SEED Award. The authors acknowledge the hospitality and support of the Aspen Center for Physics (Grant No. PHY-1607611), where part of this work was done. G. M. is grateful to the Gordon and Betty Moore Foundation for sabbatical support at MIT, and the Lady Davis Foundation for sabbatical support at the Technion. Growth of hBN crystals was supported by the Elemental Strategy Initiative conducted by the MEXT, Japan and a Grant-in-Aid for Scientific Research on Innovative Areas “Science of Atomic Layers” from JSPS. We thank the groups of J. Hone and C. Dean for experimental advice on device fabrication.
© 2020 American Physical Society.
ASJC Scopus subject areas
- Physics and Astronomy (all)