Rashba valleys and quantum Hall states in few-layer black arsenic

Feng Sheng, Chenqiang Hua, Man Cheng, Jie Hu, Xikang Sun, Qian Tao, Hengzhe Lu, Yunhao Lu, Mianzeng Zhong, Kenji Watanabe, Takashi Taniguchi, Qinglin Xia (), Zhu-An Xu () and Yi Zheng ()
Additional contact information
Feng Sheng: Zhejiang University
Chenqiang Hua: Zhejiang University
Man Cheng: Zhejiang University
Jie Hu: Zhejiang University
Xikang Sun: Zhejiang University
Qian Tao: Zhejiang University
Hengzhe Lu: Zhejiang University
Yunhao Lu: Zhejiang University
Mianzeng Zhong: Central South University
Kenji Watanabe: National Institute for Materials Science
Takashi Taniguchi: National Institute for Materials Science
Qinglin Xia: Central South University
Zhu-An Xu: Zhejiang University
Yi Zheng: Zhejiang University

Nature, 2021, vol. 593, issue 7857, 56-60

Abstract: Abstract Exciting phenomena may emerge in non-centrosymmetric two-dimensional electronic systems when spin–orbit coupling (SOC)1 interplays dynamically with Coulomb interactions2,3, band topology4,5 and external modulating forces6–8. Here we report synergetic effects between SOC and the Stark effect in centrosymmetric few-layer black arsenic, which manifest as particle–hole asymmetric Rashba valley formation and exotic quantum Hall states that are reversibly controlled by electrostatic gating. The unusual findings are rooted in the puckering square lattice of black arsenic, in which heavy 4p orbitals form a Brillouin zone-centred Γ valley with pz symmetry, coexisting with doubly degenerate D valleys of px origin near the time-reversal-invariant momenta of the X points. When a perpendicular electric field breaks the structure inversion symmetry, strong Rashba SOC is activated for the px bands, which produces spin–valley-flavoured D± valleys paired by time-reversal symmetry, whereas Rashba splitting of the Γ valley is constrained by the pz symmetry. Intriguingly, the giant Stark effect shows the same px-orbital selectiveness, collectively shifting the valence band maximum of the D± Rashba valleys to exceed the Γ Rashba top. Such an orchestrating effect allows us to realize gate-tunable Rashba valley manipulations for two-dimensional hole gases, hallmarked by unconventional even-to-odd transitions in quantum Hall states due to the formation of a flavour-dependent Landau level spectrum. For two-dimensional electron gases, the quantization of the Γ Rashba valley is characterized by peculiar density-dependent transitions in the band topology from trivial parabolic pockets to helical Dirac fermions.

Date: 2021
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DOI: 10.1038/s41586-021-03449-8

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