The thermoelectric properties of conductors with low electron density can be altered significantly by an applied magnetic field. For example, recent work has shown that Dirac and Weyl semimetals with a single pocket of carriers can exhibit a large enhancement of thermopower when subjected to a sufficiently large field that the system reaches the extreme quantum limit, in which only a single Landau level is occupied. Here we study the magnetothermoelectric properties of compensated semimetals, for which pockets of electron- and hole-type carriers coexist at the Fermi level. We show that, when the compensation is nearly complete, such systems exhibit a huge enhancement of thermopower starting at a much smaller magnetic field, such that ${\omega }_c\tau >1$, and the stringent conditions associated with the extreme quantum limit are not necessary. We discuss our results in light of recent measurements on the compensated Weyl semimetal tantalum phosphide, in which an enormous magnetothermoelectric effect was observed. We also calculate the Nernst coefficient of compensated semimetals, and show that it exhibits a maximum value with increasing magnetic field that is much larger than in the single-band case. In the dissipationless limit, where the Hall angle is large, the thermoelectric response can be described in terms of quantum Hall edge states, and we use this description to generalize previous results to the multiband case.

中文翻译：

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补偿半金属在低磁场下大幅度提高热功率

具有低电子密度的导体的热电特性可以通过施加磁场来显着改变。例如，最近的工作表明，带有单个载流子的狄拉克和魏尔半金属在受到足够大的场以至系统达到极限量子极限（其中仅占据一个朗道能级）的情况下，可以表现出极大的热功率增强。 。在这里，我们研究了补偿的半金属的磁热电特性，在费米能级上共存有电子和空穴型载流子。我们证明，当补偿接近完成时，此类系统从较小的磁场开始就表现出极大的热功率增强，从而${\omega }_C\tau >\mathrm{1个}$，并且没有必要与极端量子极限相关的严格条件。我们根据最近对补偿的Weyl半金属磷化钽进行的测量来讨论我们的结果，其中观察到了巨大的磁热电效应。我们还计算了补偿半金属的能斯特系数，并表明随着磁场的增加，它表现出的最大值比单波段情况大得多。在霍尔角较大的无耗散极限中，热电响应可以用量子霍尔边缘状态来描述，我们使用该描述将先前的结果推广到多频带情况。