Energy-resolved spin filtering effect and thermoelectric effect in topological-insulator junctions with anisotropic chiral edge states

doi:10.1007/s11467-022-1189-7

Front. Phys.

2022, Vol. 17

Issue (6) : 63504 https://doi.org/10.1007/s11467-022-1189-7

RESEARCH ARTICLE

Energy-resolved spin filtering effect and thermoelectric effect in topological-insulator junctions with anisotropic chiral edge states

Jia-En Yang¹, Hang Xie^2,³(

)

¹. School of Electronics and IoT, Chongqing College of Electronic Engineering, Chongqing 401331, China
². College of Physics, Chongqing University, Chongqing 401331, China
³. Chongqing Key Laboratory for Strongly-Coupled Physics, Chongqing University, Chongqing 401331, China

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Abstract

Topological edge states have crucial applications in the future nano spintronics devices. In this work, circularly polarized light is applied on the zigzag silicene-like nanoribbons resulting in the anisotropic chiral edge modes. An energy-dependent spin filter is designed based on the topological-insulator (TI) junctions with anisotropic chiral edge states. The resonance transmission has been observed in the TI junctions by calculating the local current distributions. And some strong Fabry−Perot resonances are found leading to the sharp transmission peaks. Whereas, the weak and asymmetric resonance corresponds to the broad transmission peaks. In addition, a qualitative relation between the resonant energy separation T_R and group velocity v_f is derived: T_R=πhv_fn/L, that indicated T_R is proportional to v_f and inversely proportional to the length L of the conductor. The different T_R between the spin-up and spin-down cases results in the energy-resolved spin filtering effect. Moreover, the intensity of the circularly polarized light can modulate the group velocity v_f. Thus, the intensity of circularly polarized light, as well as the conductor-length, play very vital roles in designing the energy-dependent spin filter. Since the transmission gap root in the Fabry−Perot resonances, the thermoelectric (TE) property can be enhanced by adjusting the gap. A schedule to enhance the TE performance in the TI-junction is proposed by modulating the electric field (E_z). The TE dependence on E_z in the nanojunction is investigated, where the appropriate E_z leads to a very high spin thermopower and spin figure of merit. These TI junctions have potential usages in the nano spintronics and thermoelectric devices.

Keywords electron transport topological edge states 2D materials spintronics thermoelectric effects

Corresponding Author(s): Hang Xie

About author:

Tongcan Cui and Yizhe Hou contributed equally to this work.

Issue Date: 15 August 2022

Cite this article:

Jia-En Yang,Hang Xie. Energy-resolved spin filtering effect and thermoelectric effect in topological-insulator junctions with anisotropic chiral edge states[J]. Front. Phys. , 2022, 17(6): 63504.

URL:

https://academic.hep.com.cn/fop/EN/10.1007/s11467-022-1189-7
https://academic.hep.com.cn/fop/EN/Y2022/V17/I6/63504

Fig.1 Schematic diagram for the ZSiNRs-based two-terminal system. The device consists of three ZSiNRs (Lead 1, Conductor, Lead 2). The real size parameters in our study are N_y = 16, and N_x changes with the need of our study. The temperature gradient

Δ T = T L − T R

is applied on two leads for the thermoelectric property calculations of the TI junctions.

Fig.2 Three types of TI edge states and their energy bands for ZSiNRs. (a) QSH state with Chern number (0, 1); (b) QAH state with Chern numbers (2, 0) (

λ Ω = − 0.15 t

); (c) QAH state with Chern numbers (−2, 0) (

λ Ω = 0.15 t

). The red (blue) arrows or bands in the figures denote the spin-up (down) case and the red and blue bands overlap in (a). The other fixed parameters in all the cases are: N_y = 16,

λ s o = 0.03 t

Fig.3 (a) Transmission spectra from Lead 1 to Lead 2 (red: spin-up; blue: spin-down; magenta: spin-polarizability). (b) Cartoon diagram of the edge states in ZSiNRs-based spin filter. (c) Local current distribution of the spin filter around the Fermi level (at E = 0.01373 eV). The fixed parameters are: N_y = 16, N_x = 40, t = 1.6 eV,

λ Ω = 0.15 t

and

λ s o = 0.03 t

Fig.4 Local current distribution for the TI junctions in Fig. 3 for different energy peaks (a) n = 2, (b) n = 3, (c) n = 4, and (d) n= 5 peaks.

Fig.5 (a−c) Transmission spectra for different lengths of conductor with a fixed light intensity: (a) 20-TI, (b) 60-TI and (c) 80-TI; (d−f) Transmission spectra for different light intensity with a fixed length of conductor (d)

λ Ω = 0.08 t

, (e)

λ Ω = 0.12 t

and (f)

λ Ω = 0.25 t

. Other fixed parameters are the same as Fig.3.

Fig.6 (a) Spin-dependent thermopower (

S σ

) and spin thermopower (

S s

) vs. the Fermi energy (E_F); (b) Spin figure of merit (Z_sT) vs. the Fermi energy E_F. The system is of 40-TI junctions with T= 50 K. Other parameters are the same as Fig. 3.

Fig.7 (a−c) The dependence of spin thermopower

S s

on the Fermi energy (E_F) with different electric fields (E_Z). (a1) and (a2) for E_Z = 0.07t/(el); (b1) and (b2) for E_Z = 0.14t/(el); (c1) and (c2) for E_Z = 0.16t/(el).

Fig.8 The spin figure of merit (Z_sT) as a function of the Fermi energy E_F with different E_Z values for 40-TI junctions.

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