Band-Gap Sensitived Seebeck Effect in Heavy Group-IV Monolayers
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EMICONDUCTORS
Band-Gap Sensitived Seebeck Effect in Heavy Group-IV Monolayers Y. Xua, b, *, X. Lia, and L. Qianc a College
of Physics Science and Technology, Yangzhou University, Yangzhou, 225002 China National Laboratory of Solid State Microstructures, Department of Physics, and Collaborative Innovation Center of Advanced Microstructures, Nanjing University, Nanjing, 210093 China c School of Physics and Electronic Engineering, Jiangsu Normal University, Xuzhou, 221116 China * e-mail: [email protected] b
Received May 5, 2020; revised June 30, 2020; accepted July 1, 2020
Abstract—We have systematically investigated the spin- and valley-dependent Seebeck effect in irradiated heavy group-IV monolayers including silicene, germanene, and stanene by means of semi-classical Boltzmann equation in diffusive regime. Due to the interplay of strong intrinsic spin-orbit coupling, perpendicular electric field, and off-resonant light field, the temperature-driven spin and valley conductivity can be controllable effectively. Except for numerical results, the amplitude of Seebeck coefficient is analyzed and found to be in direct proportion to the band gap at high temperature. It supplies a flexible method to modulate the Seebeck effect. In addition, we have compared the thermoelectric transport properties of different group-IV materials and found that the figure of merit shows great enhancement from silicene to stanene. These findings are excepted to provide a platform for the heavy group-IV materials in future spin–valley thermal and energysaving devices. Keywords: Seebeck effect, heavy group-IV materials, off-resonant light, spin and valley caloritronics DOI: 10.1134/S1063783420110402
1. INTRODUCTION Similar to C, the other elements Si, Ge, and Sn in group-IV in the periodic table are also found to exist as monolayer materials with honeycomb lattice structures, which are named silicene, germanene, and stanene [1–6]. In comparison with graphene, these materials process sp2 and sp3 orbit hybridization resulting in a low-buckled hexagonal structure. Density functional theory shows there exist large spin-orbit coupling strengths in the heavy group-IV monolayers, which are about 3.9 meV in silicene, 43 meV in germanene, and 100 meV in stanene, several orders of graphene (about 10–3 meV) [7]. The analogy between graphene and the low-buckled materials shows that the latter should be a very promising material for investigating the spin- and valley-dependent effects due to the observable spin-orbit coupling. The interplay between some external fields, such as the illumination of an intense laser, the perpendicular electric field, and the antiferromagnetic field, gives rise to various topological phase transitions, and the externalfield controlled band gap in heavy group-IV monolayers overcomes many difficulties of graphene in electronics applications. So the heavy group-IV materials aroused great interest due to their prospective properties in topologi-cal phase, spin caloritronics, and even thermoelectronics [8–13].
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