Spin polarized photoemission by optical orientation
Spin polarized photoemission by optical orientation
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DOI：
10.1016/b978-0-444-86741-4.50012-3
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发表时间：
1984
期刊：
影响因子：
--
通讯作者：
F. Meier;D. Pescia
中科院分区：
文献类型：
--
作者：
F. Meier;D. Pescia
光电子能谱是探索固体电子结构的一种强有力的方法（Cardona和Ley 1978，1979）。其中一个引人注目的成就是测量了各种材料的电子能带E（k）。从初级光电子的动能和动量中获得必要的信息。通常，没有注意到电子的内部自由度-自旋-从而放弃了对光电子状态的完整描述。在一些实验情况下，忽略尾旋不会造成严重的信息损失。然而，还有另一类光电发射实验，其中相对于适当选择的量子化方向的电子自旋方向的测量可以对固体的电子结构提供新的见解，或者可以在解释实验结果方面有所帮助。本章的目的是通过一些例子来说明这一主张。结果表明，自旋极化光电子的出现是一个相当普遍的现象。条件是用于光激发的光是圆偏振的，并且至少有一个参与跃迁的能级通过自旋-轨道相互作用从轨道简并带中分裂出来。应该指出的是，这适用于本章专门讨论的非磁性有序材料。众所周知，自旋极化光电子是使用自然的非偏振光从磁有序材料发射的：这些实验基于Siegmann及其同事的开创性工作，（Busch等人，1969年）在其他地方进行了总结（Siegmann et al.1984），下面不再考虑。固体中光学自旋取向的可行性首先由Lampel证明（Lampel 1968）。通过核磁共振检测激发电子的光致磁化。在1975年，使用低电子亲和势的重铯化GaAs，光学自旋取向的光电子被发射到真空中（Pierce和Meier 1976）。由于其有利的性质，表面活化的GaAs已被广泛用作极化电子的来源。第6章对此进行了描述。从电子光谱的观点来看，在光电发射中引入自旋极化的一个明显优点是，电子可以被除了能量和动量之外的附加量标记。调查
Photoelectron spectroscopy is a powerful method for exploring the electronic structure of solids (Cardona and Ley 1978, 1979). Among the spectacular successes is the measurement of the electronic energy bands E (k) for a variety of materials. The necessary information is obtained from the kinetic energy and momentum of the primary photoelectrons. Usually, no attention is paid to the internal degree of freedom of the electron-the spin-thereby renouncing a complete description of the state of the photoelectron. There are experimental situations where no serious loss of information is suffered by neglecting the spin. However, there is another class of photoemission experiments where the measurement of the electron spin direction with respect to a suitably chosen quantization direction can give new insights into the electronic structure of a solid or may help appreciably in interpreting experimental results. The purpose of this chapter is to illustrate this claim by a number of examples. It will be shown that the occurrence of spin polarized photoelectrons is quite a general phenomenon. The conditions are that the light used for photoexcitation is circularly polarized and that at least one of the levels involved in the transition is split off from an orbitally degenerate band by spin-orbit interaction. It should be pointed out that this applies to non-magnetically ordered materials which are exclusively dealt with in this chapter. It is well known that spin polarized photoelectrons are emitted from magnetically ordered materials using natural, unpolarized light: these experiments which are based on the pioneering work of Siegmann and coworkers (Busch et al. 1969) are summarized elsewhere (Siegmann et al. 1984) and will not be considered in the following.The feasibility of optical spin orientation in solids has first been demonstrated by Lampel (Lampel 1968). The optically induced magnetization of the excited electrons was detected by means of nuclear magnetic resonance. In 1975, using heavily cesiated GaAs of low electron affinity, optically spin oriented photoelectrons were emitted into the vacuum (Pierce and Meier 1976). Due to its favourable properties surface-activated GaAs has found widespread use as a source of polarized electrons. It is described in chapter 6. From the electron-spectroscopic point of view a clear advantage of introducing spin polarization in photoemission is the fact that electrons can be labeled by an additional quantity besides energy and momentum. Investigation of the