On the Lorenz number of multiband materials
On the Lorenz number of multiband materials
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DOI：
10.1103/physrevb.95.125206
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发表时间：
2017-03-31
影响因子：
3.7
通讯作者：
Neophytou, Neophytos
中科院分区：
文献类型：
--
作者：
Thesberg, Mischa;Kosina, Hans;Neophytou, Neophytos
威德曼-弗兰兹定律的洛伦兹数偏离预期值的情况很多。然而，在传统的半导体系统中，假设对于非简并半导体，它的值类似于1.49×10(-8)W欧米茄K-2，对于简并半导体或金属，它的值类似于2.45×10(-8)W欧米茄K-2。在许多情况下，知道洛伦兹数是很重要的，例如在热电材料的设计和晶格热导率的实验测定中。在这里，我们表明，即使在两带和三带半导体的简单情况下，也有可能获得与预期相差2倍(或者对于中间禁带附近有费米能级的双极系统，甚至是数量级)的实质性偏差。除了确定单极和双极双波段系统的偏差来源外，还导出了一些可用于量化效应大小的解析表达式。作为典型的案例研究，还建立了重要的热电材料碲化铅(PbTe)和硒化锡(SnSe)材料的三带模型，并探讨了这些材料中可能存在的洛伦兹数变化的大小。从而论证了多带效应对实系统洛伦兹数的影响。
There are many exotic scenarios where the Lorenz number of the Wiedemann-Franz law is known to deviate from expected values. However, in conventional semiconductor systems, it is assumed to vary between the values of similar to 1.49 x 10(-8)W Omega K-2 for nondegenerate semiconductors and similar to 2.45 x 10(-8)W Omega K-2 for degenerate semiconductors or metals. Knowledge of the Lorenz number is important in many situations, such as in the design of thermoelectric materials and in the experimental determination of the lattice thermal conductivity. Here, we show that, even in the simple case of two-and three-band semiconductors, it is possible to obtain substantial deviations of a factor of 2 (or in the case of a bipolar system with a Fermi level near the midgap, even orders of magnitude) from expectation. In addition to identifying the sources of deviation in unipolar and bipolar two-band systems, a number of analytical expressions useful for quantifying the size of the effect are derived. As representative case studies, a three-band model of the materials of lead telluride (PbTe) and tin sellenide (SnSe), which are important thermoelectric materials, is also developed and the size of possible Lorenz number variations in these materials explored. Thus, the consequence of multiband effects on the Lorenz number of real systems is demonstrated.