标题： 利用热电系数细化高度补偿半金属的双带模型 显示英文标题

标题： Refining the Two-Band Model for Highly Compensated Semimetals Using Thermoelectric Coefficients

摘要： 在研究补偿半金属时，两带模型已被证明在捕捉磁场下电导率（作为类电子和类空穴载流子密度和迁移率的函数）非常有用。然而，它很少能提供关于磁热电性质的实际见解。在这里，我们报道了一种高度补偿的半金属NbSb$_2$中热电（TE）系数的磁场依赖性，我们发现塞贝克系数和内斯特系数分别以二次方和线性方式随所施加磁场增加。这种磁场依赖性在先前的研究中已通过半经典玻尔兹曼输运理论预测过，前提是满足以下两个条件：$\omega_c\tau \gg 1$和$\tan\theta_H \ll 1$。在这种情况下，我们发现TE系数的磁场依赖性直接提供了类电子（$n_e$）和类空穴（$n_h$）载流子密度之间的关系，这反过来可以用于改进两带模型拟合。通过这种方法，我们发现NbSb$_2$的补偿因子（$\frac{|\Delta n|}{n_e}$）比无限制拟合中发现的值小两个数量级，导致磁阻的饱和场尺度更大。 在同一半经典理论框架内，我们还推导出热电霍尔角 $\tan\theta_{\gamma} = \frac{S_{xy}}{S_{xx}}$ 可以表示为 $\big(\frac{|\Delta n|}{n_e} \times \omega_c\tau\big)^{-1}$，这作为一个参数来预测补偿的程度。 我们的发现为识别场致增强热电性能的经验条件以及基于半金属材料设计高效热电装置提供了重要的见解。 显示英文摘要

摘要： In studying compensated semimetals, the two-band model has proven extremely useful in capturing electrical conductivity under magnetic field, as a function of density and mobility of electron-like and hole-like carriers. However, it rarely offers practical insight into magneto-thermoelectric properties. Here, we report the field dependence of thermoelectric (TE) coefficients in a highly compensated semimetal NbSb$_2$, where we find the Seebeck and Nernst coefficients increase quadratically and linearly with applied magnetic field, respectively. Such field dependence was predicted in previous work that studied a system of two parabolic bands, within semiclassical Boltzmann transport theory when the following two conditions are simultaneously met:$\omega_c\tau \gg 1$ and $\tan\theta_H \ll 1$. Under these conditions, we find the field dependence of the TE coefficients directly provides a relation between the electron-like ($n_e$) and hole-like ($n_h$) carrier densities, which in turn can be used to refine two-band model fitting. With this, we find the compensation factor ($\frac{|\Delta n|}{n_e}$) of NbSb$_2$ is two orders of magnitude smaller than what was found in unrestricted fitting, resulting in a larger saturation field scale for magnetoresistance. Within the same framework of the semiclassical theory, we also deduce that the thermoelectric Hall angle $\tan\theta_{\gamma} = \frac{S_{xy}}{S_{xx}}$ can be expressed as $\big(\frac{|\Delta n|}{n_e} \times \omega_c\tau\big)^{-1}$, which serves as a parameter to predict the degree of compensation. Our findings offer crucial insights into identifying empirical conditions for field-induced enhancement of TE performance and into engineering efficient thermoelectric devices based on semimetallic materials.