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Electric control of topological phase transitions in Dirac semimetal thin films.

Pan H, Wu M, Liu Y, Yang SA - Sci Rep (2015)

Bottom Line: 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.

View Article: PubMed Central - PubMed

Affiliation: Department of Physics, Beihang University, Beijing 100191, China.

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.

No MeSH data available.


Calculated LDOS of a side surface for Na3Bi thin film.(a) is for point A (trivial insulator) and (b) is for point C (QSH insulator) as marked in Fig. 1(a). The calculation is for a slab which is semi-infinite along y-direction and the parameters are the same as for Fig. 1.
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f2: Calculated LDOS of a side surface for Na3Bi thin film.(a) is for point A (trivial insulator) and (b) is for point C (QSH insulator) as marked in Fig. 1(a). The calculation is for a slab which is semi-infinite along y-direction and the parameters are the same as for Fig. 1.

Mentions: To further demonstrate the topological nature of the transition and to visualize the edge states, we compute the surface local density of states (LDOS) for the side surface. Due to the isotropy in the kx–ky plane of the low-energy model (1), without loss of generality, we choose the surface perpendicular to y-direction of the quasi-2D system. The surface LDOS ρ(kx) can be calculated for each kx from the surface Green’s function , where G00 is the retarded Green’s function for the surface layer (labled by index 0) of the lattice36. G00 can be evaluated by the transfer matrix through a standard numerical iterative method37. The obtained surface LDOS for states before and after the phase transition (for state A and C) are plotted in Fig. 2. One observes that for both cases, the confinement-induced bulk gap can be clearly identified. Before the topological phase transition (E < Ec), there is no states inside the gap. In contrast, after transition (E > Ec), there appear two bright lines crossing the gap, corresponding to the spin helical edge states for the nontrivial QSH phase. As long as time reversal symmetry is preserved, these gapless modes are protected and carriers in these channels cannot be backscattered12. Therefore transport through these channels is in principle dissipationless. In a two-terminal measurement, this would lead to a quantized conductance, which has been confirmed experimentally3.


Electric control of topological phase transitions in Dirac semimetal thin films.

Pan H, Wu M, Liu Y, Yang SA - Sci Rep (2015)

Calculated LDOS of a side surface for Na3Bi thin film.(a) is for point A (trivial insulator) and (b) is for point C (QSH insulator) as marked in Fig. 1(a). The calculation is for a slab which is semi-infinite along y-direction and the parameters are the same as for Fig. 1.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4588596&req=5

f2: Calculated LDOS of a side surface for Na3Bi thin film.(a) is for point A (trivial insulator) and (b) is for point C (QSH insulator) as marked in Fig. 1(a). The calculation is for a slab which is semi-infinite along y-direction and the parameters are the same as for Fig. 1.
Mentions: To further demonstrate the topological nature of the transition and to visualize the edge states, we compute the surface local density of states (LDOS) for the side surface. Due to the isotropy in the kx–ky plane of the low-energy model (1), without loss of generality, we choose the surface perpendicular to y-direction of the quasi-2D system. The surface LDOS ρ(kx) can be calculated for each kx from the surface Green’s function , where G00 is the retarded Green’s function for the surface layer (labled by index 0) of the lattice36. G00 can be evaluated by the transfer matrix through a standard numerical iterative method37. The obtained surface LDOS for states before and after the phase transition (for state A and C) are plotted in Fig. 2. One observes that for both cases, the confinement-induced bulk gap can be clearly identified. Before the topological phase transition (E < Ec), there is no states inside the gap. In contrast, after transition (E > Ec), there appear two bright lines crossing the gap, corresponding to the spin helical edge states for the nontrivial QSH phase. As long as time reversal symmetry is preserved, these gapless modes are protected and carriers in these channels cannot be backscattered12. Therefore transport through these channels is in principle dissipationless. In a two-terminal measurement, this would lead to a quantized conductance, which has been confirmed experimentally3.

Bottom Line: 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.

View Article: PubMed Central - PubMed

Affiliation: Department of Physics, Beihang University, Beijing 100191, China.

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.

No MeSH data available.