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混合型量子点系统是研究热电转换机制的良好平台.本文提出了一个含自旋-轨道作用的双量子点耦合金属和超导体构成的混合型系统模型,进而研究该混合型系统的电荷以及自旋热电输运特征.我们深入讨论了热电系数与系统参数之间的关系,发现系统存在显著的魏德曼-弗兰兹定律违背现象,这有助于增强热电转换效率.更重要的是,由于存在超导体能隙外的准粒子隧穿,这个混合型热电器件能够产生纯自旋塞贝克效应.在实践上,这个效应可以被利用设计和制造一个纯自旋流发生器.在线性响应机制下,我们也讨论了该混合型热电系统作为一个热机的热力学性能.本文的研究结果对于理解混合型热电系统的热电转换特征及其热力学性能具有理论和实践意义.The normal metal-quantum dots-superconductor hybrid system is a good platform to study the mechanism of thermoelectric conversion. In terms of non-equilibrium Keldysh Green's function formalism and linear response theory, the charge and spin thermoelectric transport characteristics of a normal-double quantum dot-superconductor hybrid system with spin-orbit coupling are studied in this paper. We deeply discuss the relationship between thermoelectric coefficients and the system parameters, and find both charge and spin thermoelectric coefficients exhibit distinct symmetry characteristics in the parameter space composed of temperature and energy. An increase in temperature leads to a decrease in the conductance within the energy gap, which is attributed to a reduction in Andreev transport. However, outside the energy gap, the conductance gradually increases, and the thermal conductance is gradually enhanced. This is because more quasiparticles outside the energy gap participate in thermoelectric transport, and a large charge thermopower is generated in the region far from the energy gap. It is found that the thermoelectric figure of merit is greater than 1, indicating a strong violation of the Wiedemann-Franz law. With the increase of temperature, the large spin thermopower as well as spin thermoelectric figure of merit can be obtained outside the energy gap. The charge (spin) thermopower and the thermoelectric figure of merit show the rich evolutionary characteristics as functions of the energy level and the Zeeman energy. With the disappearance of the charge thermopower, the spin thermopower still has a finite value, which leads to the emergence of a pure spin Seebeck effect. This is helpful for designing a pure spin current thermoelectric generator. Due to a competitive mechanism between the spin-orbit coupling effect and the Zeeman field, thermoelectric coefficients are decreased with increasing the strength of spin-orbit interaction, but one still can obtain the spin thermoelectric quantities which meet the practical needs by regulating the strength of spin-orbit coupling and the Zeeman energy. The evolution pattern of the thermoelectric coefficients in the energy space indicates that the enhancement of thermoelectric conversion efficiency can be achieved by modulating the energy levels of double quantum dots. In addition, this hybrid system can function as a heat engine to achieve the conversion of heat to work. Although its power and efficiency do not evolve synchronously, in some parameter regions, people can still obtain the thermodynamic performance that meets practical needs. The research results of this paper hold theoretical and practical significance for understanding the thermoelectric transport and thermodynamic performance of hybrid thermoelectric systems.
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Keywords:
- Hybrid quantum dot system /
- Spin-orbit coupling /
- Thermoelectric transport /
- Power and efficiency
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