Intrinsic coupling between spatially-separated surface Fermi-arcs in Weyl orbit quantum Hall states

Shinichi Nishihaya,Yusuke Nakazawa,Markus Kriener,Yasujiro Taguchi,Masaki Uchida,Masashi Kawasaki

doi:10.1038/s41467-021-22904-8

Abstract

Topological semimetals hosting bulk Weyl points and surface Fermi-arc states are expected to realize unconventional Weyl orbits, which interconnect two surface Fermi-arc states on opposite sample surfaces under magnetic fields. While the presence of Weyl orbits has been proposed to play a vital role in recent observations of the quantum Hall effect even in three-dimensional topological semimetals, actual spatial distribution of the quantized surface transport has been experimentally elusive. Here, we demonstrate intrinsic coupling between two spatially-separated surface states in the Weyl orbits by measuring a dual-gate device of a Dirac semimetal film. Independent scans of top- and back-gate voltages reveal concomitant modulation of doubly-degenerate quantum Hall states, which is not possible in conventional surface orbits as in topological insulators. Our results evidencing the unique spatial distribution of Weyl orbits provide new opportunities for controlling the novel quantized transport by various means such as external fields and interface engineering.

Highlights

Topological semimetals hosting bulk Weyl points and surface Fermi-arc states are expected to realize unconventional Weyl orbits, which interconnect two surface Fermi-arc states on opposite sample surfaces under magnetic fields
Quantum oscillations in the resistance Rxx are clearly observed in both transverse (I ⊥ B) and longitudinal (I ∥ B) field configurations, which ensures that the film is thick enough to keep the 3D bulk state with gapless bulk nodes required for the formation of the Weyl orbit
Our results provide transport evidence of an intrinsic coupling between the two spatially separated surface states in the presence of Weyl orbits

Summary

Introduction

Topological semimetals hosting bulk Weyl points and surface Fermi-arc states are expected to realize unconventional Weyl orbits, which interconnect two surface Fermi-arc states on opposite sample surfaces under magnetic fields. While the presence of Weyl orbits has been proposed to play a vital role in recent observations of the quantum Hall effect even in threedimensional topological semimetals, actual spatial distribution of the quantized surface transport has been experimentally elusive. Distinct from the 2D bulk transport triggered by sub-band splitting under confinement[15,16], the 2D surface transport is typically accompanied by coexisting 3D bulk state, and is characterized by a larger Fermi surface and band mass than their bulk counterparts[10,11,12,13,14] It exhibits quantum oscillations, and quantum Hall (QH) effect in high magnetic fields or at low carrier concentrations[12,13,14], attracting growing attention as novel quantized transport in a 3D system. It is challenging to verify the existence of Weyl orbits, excluding extrinsic origins

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Conclusion