New approaches to injecting spin polarized currents into semiconductors

任何基于半导体自旋电子学的技术的详细阐述的一个关键因素是可靠地将可调极化的自旋电流注入半导体器件的可能性。自旋注入先前已被证明使用体DMS注入层1或共振隧穿二极管2。这些方法中的第一种需要厚层，因此不太可能用于调谐电路的各种元件之间的自旋极化电流，而这些方法中的第二种需要复杂且优化良好的层结构，这带来了严重的集成挑战。在本建议中，我们的目标是研究两种替代方法，这已经在文献中提出的理论，产生自旋极化电流。第一种是使用单个磁势垒作为自旋过滤器3，第二种是电控自旋场效应晶体管4，它允许我们在固定磁场中调节电流的极化。与往常一样，在进行自旋极化电流实验时，其中一个挑战在于检测注入效率。通常，可观察到的直接输运是磁阻，然后使用给定的输运模型将其反算为自旋极化。由于这些模型通常做出不容易验证的假设，例如自旋散射长度，这通常会导致关于极化电流是否真正注入的模糊性。为了解决这个问题，我们提出了一个免费使用的运输和光学技术，研究在运输中的磁阻现象，并确认通过直接光学检测使用磁光克尔效应测量的载波的偏振的解释。

A key ingredient for the elaboration of any semiconductor spintronics based technology is the possibility of reliable injecting a spin current of tunable polarization into the semiconductor devices. Spin injection has previously been demonstrated using bulk DMS injector layers1 or resonant tunneling diodes2. The first of these methods requires thick layers and is therefore unlikely to be useful for the tuning of spin polarized currents between various elements of a circuit, whereas the second of these methods requires a complex and well optimized layer structure which presents serious integration challenges. In the present proposal we aim to study two alternative methods, which have been theoretically proposed in the literature, to produce spin polarized currents. The first is the use of a single magnetic barrier as a spin filter3 and the second is an electrically controlled spin field effect transistor4 which would allow us to tune the polarization of the current in a fixed magnetic field. As always when working on experiments with spin polarized current, one of the challenges lies in the detection of the injection efficiency. Often, the direct transport observable is a magnetoresistance, which is then back calculated into a spin polarization using a given transport model. Since these models typically make assumptions that are not easily verified on, for example, spin scattering lengths, this can often lead to ambiguity as to whether a polarized current is truly injected. In order to address this issue, we propose a complimentary use of transport and optical techniques, studying the magnetoresistance phenomena in transport and confirming the interpretation by direct optical detection of the polarization of the carrier using magnetooptical Kerr effect measurements.