Abstract
Dirac semimetals host three-dimensional (3D) Dirac fermion states in the bulk of crystalline solids, which can be viewed as 3D analogs of graphene. Owing to their relativistic spectrum and unique topological character, these materials hold great promise for fundamental-physics exploration and practical applications. Particularly, they are expected to be ideal parent compounds for engineering various other topological states of matter. In this report, we investigate the possibility to induce and control the topological quantum spin Hall phase in a Dirac semimetal thin film by using a vertical electric field. We show that through the interplay between the quantum confinement effect and the field-induced coupling between sub-bands, the sub-band gap can be tuned and inverted. During this process, the system undergoes a topological phase transition between a trivial band insulator and a quantum spin Hall insulator. Consequently, one can switch the topological edge channels on and off by purely electrical means, making the system a promising platform for constructing topological field effect transistors.
Highlights
It has been shown that with increasing thickness, DSM thin films exhibit oscillations in the 2D 2 invariant whenever a quantum well state crosses the Dirac point[10,31]
Motivated by these recent breakthroughs and by the great interest in utilizing DSMs for topological devices, in this work, we investigate the possibility of electric control of the topological phase transitions in a DSM thin film
We show that by using a vertical electric field, DSM thin films can be switched between a topological quantum spin Hall (QSH) phase and a trivial insulator phase
Summary
Our analysis is based on a generic low-energy effective model describing the DSMs A3Bi (A = N a, K, Rb) and Cd3As2 as derived in previous works[9,10]. In these materials, the states around Fermi energy can be expanded using a minimal four-orbital basis of S1/2, 1/2 , P3/2, 3/2 , S1/2, −1/2 , and P3/2, −3/2. It is because backscattering can occur between edge states from different time reversal pairs Following this logic, the topological properties as well as the bulk band gap show oscillatory behavior as a function of the film thickness[10,31].
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