RESUMO
The exotic topological surface states of Dirac or Weyl semimetals, namely Fermi arcs, are predicted to be spin polarized, while their spin polarization nature is still not revealed by transport measurements. Here, we report the spin-polarized transport in a Dirac semimetal Cd_{3}As_{2} nanowire employing the ferromagnetic electrodes for spin detection. The spin-up and spin-down states can be changed by reversing the current polarity, showing the spin-momentum locking property. Moreover, the nonlocal measurements show a high fidelity of the spin signals, indicating the topological protection nature of the spin transport. As tuning the Fermi level away from the Dirac point by gate voltages, the spin signals gradually decrease and finally are turned off, which is consistent with the fact that the Fermi arc surface state has the maximum ratio near the Dirac point and disappears above the Lifshitz transition point. Our results should be valuable for revealing the transport properties of the spin-polarized Fermi arc surface states in topological semimetals.
RESUMO
The quantum Hall effect (QHE) in a 3D Dirac semimetal thin film is attributed to either the quantum confinement induced bulk subbands or the Weyl orbits that connect the opposite surfaces via bulk Weyl nodes. However, it is still unknown whether the QHE based on the Weyl orbit can survive as the bulk Weyl nodes are gapped. Moreover, there are closed Fermi loops rather than open Fermi arcs on the Dirac semimetal surface, which can also host the QHE. Here we report the QHE in the 3D Dirac semimetal Cd_{3}As_{2} nanoplate by tuning the gate voltage under a fixed 30 T magnetic field. The quantized Hall plateaus at odd filling factors are observed as a magnetic field along the [001] crystal direction, indicating a Berry's phase π from the topological surface states. Furthermore, even filling factors are observed when the magnetic field is along the [112] direction, indicating the C_{4} rotational symmetry breaking and a topological phase transition. The results shed light on the understanding of QHE in 3D Cd_{3}As_{2}.
RESUMO
Dirac semimetals possess Fermi-arc surface states, which will be a set of discrete surface subbands in a nanowire due to the quantum confinement effect. Here, we report a tunable Fano effect induced by the interference between the discrete surface states and continuous bulk states of a Dirac semimetal Cd_{3}As_{2} nanowire. The discrete surface bands lead to a zero bias peak in conductance as the Femi level is tuned to across the surface subbands. The Fano resonance results in an asymmetric line shape in the differential conductance dI/dV spectrum. Furthermore, the Fano interference would introduce an additional phase into the Weyl orbits and lead to a modification of the oscillation frequency. The results are valuable for further understanding the exotic quantum transport properties of topological semimetals.
RESUMO
It has been theoretically proposed that the spin textures of surface states in a topological insulator can be directly transferred to graphene by means of the proximity effect, which is very important for realizing a two-dimensional topological insulator based on graphene. Here we report the anomalous magnetotransport properties of graphene-topological insulator Bi2Se3 heterojunctions, which are sensitive to the electronic coupling between graphene and the topological surface state. The coupling between the pz orbitals of graphene and the p orbitals of the surface states on the Bi2Se3 bottom surface can be enhanced by applying a perpendicular negative magnetic field, resulting in a giant negative magnetoresistance at the Dirac point up to about -91%. An obvious resistance dip in the transfer curve at the Dirac point is also observed in the hybrid devices, which is consistent with theoretical predictions of the distorted Dirac bands with nontrivial spin textures inherited from the Bi2Se3 surface states.
RESUMO
[This corrects the article DOI: 10.1371/journal.pone.0156756.].