Materials with spin-orbit coupling are of great interest for various spintronics applications due to the efficient electrical generation and detection of spin-polarized electrons. Over the past decade, many materials have been studied, including topological insulators, transition metals, Kondo insulators, semimetals, semiconductors, and oxides; however, there is no unifying physical framework for understanding the physics and therefore designing a material system and devices with the desired properties. We present a model that binds together the experimental data observed on the wide variety of materials in a unified manner. We show that in a material with a given spin-momentum locking, the density of states plays a crucial role in determining the charge-spin interconversion efficiency, and a simple inverse relationship can be obtained. Remarkably, experimental data obtained over the last decade on many different materials closely follow such an inverse relationship. We further deduce two figure of merits of great current interest: the spin-orbit-torque (SOT) efficiency (for the direct effect) and the inverse Rashba-Edelstein effect length (for the inverse effect), which statistically show good agreement with the existing experimental data on wide varieties of materials. Particularly, we identify a scaling law for the SOT efficiency with respect to the carrier concentration in the sample, which agrees with existing data. Such an agreement is intriguing since our transport model includes only Fermi surface contributions and fundamentally different from the conventional views of the SOT efficiency that includes contributions from all the occupied states.

中文翻译：

---

自旋轨道材料中电荷自旋互变的统一框架

由于自旋极化电子的有效发电和检测，具有自旋轨道耦合的材料对于各种自旋电子学都引起了极大的兴趣。在过去的十年中，已经研究了许多材料，包括拓扑绝缘体，过渡金属，近藤绝缘体，半金属，半导体和氧化物。但是，没有统一的物理框架来理解物理学，因此没有设计具有所需特性的材料系统和设备。我们提出了一个模型，该模型以统一的方式将在各种材料上观察到的实验数据绑定在一起。我们表明，在具有给定自旋动量锁定的材料中，态密度在确定电荷-自旋互变效率中起着至关重要的作用，并且可以获得简单的逆关系。值得注意的是 过去十年间在许多不同材料上获得的实验数据紧密地遵循了这种反比关系。我们进一步推论出两个当前具有重大意义的优点：自旋-轨道-转矩（SOT）效率（用于直接效应）和逆Rashba-Edelstein效应长度（用于逆效应），它们在统计上显示出与现有的有关各种材料的实验数据。特别是，我们确定了样品中载流子浓度相对于SOT效率的缩放定律，该定律与现有数据一致。这样的协议很有趣，因为我们的运输模型仅包括费米表面贡献，并且与SOT效率的传统观点（包括所有被占州的贡献）根本不同。