Cd 3 As 2 is a model material of Dirac semimetal with a linear dispersion relation along all three directions in the momentum space. The unique band structure of Cd 3 As 2 makes it with both Dirac and topological properties. It can be driven into a Weyl semimetal by the symmetry breaking or a topological insulator by enhancing the spin-orbit coupling. Here we report the temperature and gate voltage dependent magnetotransport properties of Cd 3 As 2 nanoplates with Fermi level near the Dirac point. The Hall anomaly demonstrates the two-carrier transport accompanied by a transition from n-type to p-type conduction with decreasing temperature. The carrier-type transition is explained by considering the temperature dependent spin-orbit coupling. The magnetoresistance exhibits a large non-saturating value up to 2000% at high temperatures, which is ascribed to the electron-hole compensation in the system. Our results are valuable for understanding the experimental observations related to the two-carrier transport in Dirac/Weyl semimetals, such as Na 3 Bi, ZrTe 5 , TaAs, NbAs, and HfTe 5 .KEYWORDS: Dirac semimetal, magnetoresistance, two-band transport, temperature dependence, Hall resistance Three-dimensional (3D) Dirac semimetal 1-3 is a quantum material, where the conduction bands and valence bands touch at discrete points, known as Dirac points.In momentum space, it has linear dispersion along all three directions near the Dirac points, which are protected by the rotational crystalline symmetry. 3,4 Upon breaking of time-reversal symmetry or spatial inversion symmetry, the Dirac point splits into a pair of Weyl nodes with opposite chiralities, thus the Dirac semimetal changes into Weyl semimetal. 5,6 The distinct electronic structures of Dirac semimetal give rise to many other topological phases, for examples, topological insulator 7,8 and topological superconductor. 9 Recently, the negative magnetoresistance (MR) has been observed in Dirac semimetal 10-13 and Weyl semimetal, 14 which is attributed to the chiral anomaly in the presence of parallel electric field and magnetic field. 15,16 In the family of 3D Dirac semimetal, Cd 3 As 2 is a model material that has a pair of Dirac points near the Γ point in the Brillouin zone. 3,[17][18][19] Angle-resolved photoemission spectroscopy (ARPES) and scanning tunneling microscopy both reveal the linear dispersion near the Dirac ResultsNanoplate Characterizations. The as-grown Cd 3 As 2 nanoplates are single crystalline. 31 As shown in Figure 1a, the scanning electron microscopy (SEM) image indicates that the lateral dimension of the nanoplates ranges from several micrometers to tens of micrometers. A corner of a typical nanoplate is shown by the transmission electron microscopy (TEM) image in Figure 1b. The high-resolution TEM image in Si substrate with 285 nm SiO 2 thin layer serves as the back gate. Figure 2b shows the temperature dependence of the longitudinal resistivity, which exhibits a semiconducting behavior at high temperatures and a metallic behavi...

No abstract

Dirac semimetals [1], such as Cd 3 As 2 or Na 3 Bi [2][3][4][5][6][7][8][9][10], show a linear electronic dispersion in three dimensions described by two copies of the Weyl equation. Applying a magnetic field can break the time reversal symmetry, and the Dirac semimetal is transformed into a Weyl semimetal with the two Weyl nodes separated in the momentum space [10,11]. Chiral charge pumping between the Weyl nodes with different chirality is predicted, which brings the Weyl fermions into the experimental realm. Recently, anomalous transport properties signaled by a pronounced negative magnetoresistance are observed as the evidence for the chiral anomaly effect [10,12].Besides this, the surface dispersion-relation of a Weyl semimetal is topologically equivalent to a non-compact Riemann surface without equal-energy contour that encloses the projection of the Weyl point [13], leading to the emergence of surface Fermi arcs [14]. Lots of angle-resolved photoemission spectroscopy (ARPES) experiments [7,[15][16][17][18] [16,19,[32][33][34][35][36][37][38]. Although the one-dimensional helical transport has been demonstrated in topological insulator nanowires through measuring the AB oscillations is the flux quantum and , where is the measured magnetic field periodicity ( in this case) and S is the cross-sectional area.From the magnetic field periodicity, we can deduce the cross-sectional area to be , which is consistent with the nanowire diameter ~58 nm. In To further clearly present the conductance oscillations, we plot the mapping of ∆G versus gate voltage and magnetic field in Fig. 1d. Clearly there are two kinds of phase modulations on the interference. One is tuned by gate voltage, and the other is influenced by the magnetic field. At a fixed gate voltage, if the conductance reaches the minimum at zero magnetic field, the conductance will be the maximum at half integer multiple of ; if the conductance is maximum at zero magnetic field, the conductance will be the maximum at integer multiple of . The phase of the AB interference is strongly dependent on gate voltage. while when the chirality is -1, the energy dispersion has a similar form with a sign 6 change. This physics picture is depicted in Fig. 2. At zero magnetic field, that is =0, the original linear energy dispersion becomes gapped with a series of sub-bands, as shown in Fig. 2a. The red and blue lines represent the chirality to be +1 and -1, respectively. According to the surface band splitting, there should emerge a periodic oscillation when the Fermi level crosses the sub-bands continuously. This is what happens in our Cd 3 As 2 nanowires, as shown in Fig. 1b.When a magnetic field is applied, the corresponding AB oscillation term should be considered. The surface energy band diagrams at the magnetic flux and are depicted in Fig. 2b, where the letter L and R denote the chirality of Weyl nodes to be +1 or −1. Apparently, when the magnetic flux is half integer of Ф 0 , the linear energy band with specified chirality emerges. The quantum transport can be...

No abstract

Various novel physical properties have emerged in Dirac electronic systems, especially the topological characters protected by symmetry. Current studies on these systems have been greatly promoted by the intuitive concepts of Berry phase and Berry curvature, which provide precise definitions of the topological orders. In this topical review, transport properties of topological insulator (Bi 2 Se 3 ), topological Dirac semimetal (Cd 3 As 2 ) and topological insulator-graphene heterojunction are presented and discussed. Perspectives about transport properties of two-dimensional topological nontrivial systems, including topological edge transport, topological valley transport and topological Weyl semimetals, are provided.