量子热电输运中互易关系的实验验证
Experimental verification of reciprocity relations in quantum thermoelectric transport
摘要：
对称关系是基本原理的体现，是现代物理学的基石。一个例子是连接热力学通量和力的系数之间的昂萨格关系，中央运输理论和实验。这些互易关系最初是为经典系统而制定的，在量子导体中也得到了满足。令人惊讶的是，新的关系已被预测专门用于热电传输。然而，尽管这些热电互易关系迄今尚未得到验证，但它们已被预测为对非弹性散射敏感，总是存在于有限温度下。这些关系在实践中是否存在的问题对热电性很重要：尽管它们的存在可以简化复杂热电材料的理论，但它们的缺失已被证明在原则上能够实现给定材料质量的更高的热电能量转换效率。在这里，我们通过实验验证了四端介观器件中的热电互易关系，其中每个端子都可以单独进行电偏置和热偏置。在同时反转磁场和交换注入和发射接触的情况下，线性响应热电系数是对称的。有趣的是，我们还观察到的互易关系的故障作为增加热偏压的函数。因此，我们的测量清楚地建立了热电互易关系的存在，以及控制其击穿以提高热电性能的可能性
英文摘要：
Symmetry relations are manifestations of fundamental principles and constitute cornerstones of modern physics. An example are the Onsager relations between coefficients connecting thermodynamic fluxes and forces, central to transport theory and experiments. Initially formulated for classical systems, these reciprocity relations are also fulfilled in quantum conductors. Surprisingly, novel relations have been predicted specifically for thermoelectric transport. However, whereas these thermoelectric reciprocity relations have to date not been verified, they have been predicted to be sensitive to inelastic scattering, always present at finite temperature. The question whether the relations exist in practice is important for thermoelectricity: whereas their existence may simplify the theory of complex thermoelectric materials, their absence has been shown to enable, in principle, higher thermoelectric energy conversion efficiency for a given material quality. Here we experimentally verify the thermoelectric reciprocity relations in a four-terminal mesoscopic device where each terminal can be electrically and thermally biased, individually. The linear response thermoelectric coefficients are found to be symmetric under simultaneous reversal of magnetic field and exchange of injection and emission contacts. Intriguingly, we also observe the breakdown of the reciprocity relations as a function of increasing thermal bias. Our measurements thus clearly establish the existence of the thermoelectric reciprocity relations, as well as the possibility to control their breakdown with the potential to enhance thermoelectric performance
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