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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 Cd3As2 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 Cd3As2 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.
Highlights
Unconventional surface states protected by non-trivial bulk orders are sources of various exotic quantum transport in topological materials
This unique connectivity enables the formation of an exotic orbit (Weyl orbit), where two Fermi-arcs on opposite surfaces are interconnected by bulk chiral modes (N = 0 Landau levels) transferring electrons across the slab thickness[5] (Fig. 1b), leading to the experimental detection of quantum oscillations[6,7,8]
As originally predicted for quantum oscillations[5], the existence of an additional phase term resulting from the bulk tunneling process can be a clear indication of Weyl orbit transport, though it is still questionable and not theoretically verified whether such a phase term originating from the bulk state can be even applied to quantum Hall effect where exact quantization of electron phases within a two-dimensional (2D) gapped energy structure is necessary
Summary
Unconventional surface states protected by non-trivial bulk orders are sources of various exotic quantum transport in topological materials. The recent theoretical prediction of Weyl orbit quantization[9,10] and the following experimental observation of quantum Hall (QH) states in bulk nano-plates of the DSM Cd3As27,11,12 has provoked further interest in the novel quantization physics in three-dimensional (3D) topological semimetals.
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