Anisotropic magnetoelectronic structures and magneto-transport properties of topological Dirac semimetal nanowires

Abstract

Abstract The magnetoelectronic structures, and the charge and spin conductance spectra of topological Dirac semimetal (TDS) nanowires are calculated by adopting the tight-binding Hamiltonian model in combination with the Green’s-function-based Landauer-Buttiker formula. Anisotropic electronic structures and magneto-transport properties are found in TDS nanowires with different confinement and magnetic field directions. With respect to in-plane-confinement TDS nanowires, trivial surface/corner states are observed and they are split into two spin-polarized states with oppositive signs when a weak out-of-plane magnetic field is applied. Moreover, the spin-polarized surface states will be transformed into bulk and corner states as the magnetic field strength is increased. Therefore, quantized spin conductance energy windows and fully-spin-polarized conductance can be achieved in the normal/out-of-plane-magnetic-field-modulated/normal TDS system in the case of the weak and strong fields, respectively. However, chiral surface states are generated when an in-plane magnetic field is applied, resulting in the perfect charge conductance steps of the normal/in-plane-magnetic-field-modulated/normal TDS system. With respect to the TDS nanowire with both the in-plane and out-of-plane confinements, nontrivial spin-momentum-locked helical surface states are observed. However, the helical character of the surface states will be destroyed and nontrivial-trivial topological phase transition happens as a high in-plane magnetic field is applied. In addition, the energy position of the surface subband inside the bulk energy gap is shifted so that the surface state transport can be switched on or off by tuning the magnetic field strength. Interestingly, the surface subband situated inside the bulk energy gap is split into two subbands with opposite spin signs as an out-of-plane magnetic field is added. Therefore, the topological phase transition between the quantum spin Hall and spin-polarized quantum Hall phases in the TDS nanowire, and the spin-polarized transport in the normal/out-of-plane-magnetic-field-modulated/normal TDS system, can be controlled by varying the magnetic field strength. These effects may benefit both the fundamental understanding of the magneto-electronic characters of the TDS nanostructures and the design of low-dissipation (spin) electronic devices.