Quantized surface transport in topological Dirac semimetal films

Abstract

Unconventional surface states protected by non-trivial bulk orders are sources of various exotic quantum transport in topological materials. One prominent example is the unique magnetic orbit, so-called Weyl orbit, in topological semimetals where two spatially separated surface Fermi-arcs are interconnected across the bulk. The recent observation of quantum Hall states in Dirac semimetal Cd 3 As 2 bulks have drawn attention to the novel quantization phenomena possibly evolving from the Weyl orbit. Here we report surface quantum oscillation and its evolution into quantum Hall states in Cd 3 As 2 thin film samples, where bulk dimensionality, Fermi energy, and band topology are systematically controlled. We reveal essential involvement of bulk states in the quantized surface transport and the resultant quantum Hall degeneracy depending on the bulk occupation. Our demonstration of surface transport controlled in film samples also paves a way for engineering Fermi-arc-mediated transport in topological semimetals.

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

“…3 and 4 indicate that the field-induced splitting of the paired Weyl orbits in DSM plays a critical role in determining the detailed appearance of the QH filling factors. We therefore suggest that the Weyl orbit degeneracy lifting sensitive to external fields may also explain the variation in the previous observations 10, [12][13][14] .…”

“…As proposed based on a semiclassical picture, the bulk tunneling process may be experimentally detectable as phase shift of QH plateaus when the bulk thickness is modulated 4,5,12 . It should be noted, though, that a similar plateau shift can be induced also by inhomogeniety of sheet carrier density which varies proportionally to the thickness 13,14 . Therefore, it is challenging to verify the existence of Weyl orbits excluding extrinsic origins.…”

“…Experimentally, transport signatures of the 2D surface states have been reported by several groups [9][10][11][12][13][14] , mainly for the typical DSM material Cd 3 As 2 . Distinct from the bulk transport under confinement 15,16 , the surface transport is characterized by a larger Fermi surface and band mass than their bulk counterparts [10][11][12][13][14] . It exhibits not only quantum oscillations but also 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.…”

“…In previous studies of the surface QH states 10,[12][13][14] , observed QH filling factors and degeneracy greatly differ by experimental setups. This variation has been hindering the consistent understanding of the quantized transport.…”

“…Distinct from the bulk transport under confinement 15,16 , the surface transport is characterized by a larger Fermi surface and band mass than their bulk counterparts [10][11][12][13][14] . It exhibits not only quantum oscillations but also 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. On the other hand, an important question still under debate is whether the two opposite surface states are coupled through the bulk nodes in the quantized state.…”