Spintronics: Fundamentals and applications

Spintronics, or spin electronics, involves the study of active control and manipulation of spin degrees of freedom in solid-state systems. This article reviews the current status of this subject, including both recent advances and well-established results. The primary focus is on the basic physical principles underlying the generation of carrier spin polarization, spin dynamics, and spin-polarized transport in semiconductors and metals. Spin transport differs from charge transport in that spin is a nonconserved quantity in solids due to spin-orbit and hyperfine coupling. The authors discuss in detail spin decoherence mechanisms in metals and semiconductors. Various theories of spin injection and spin-polarized transport are applied to hybrid structures relevant to spin-based devices and fundamental studies of materials properties. Experimental work is reviewed with the emphasis on projected applications, in which external electric and magnetic fields and illumination by light will be used to control spin and charge dynamics to create new functionalities not feasible or ineffective with conventional electronics.Comment: invited review, 36 figures, 900+ references; minor stylistic changes from the published versio

Semiconductor Spintronics

Spintronics refers commonly to phenomena in which the spin of electrons in a solid state environment plays the determining role. In a more narrow sense spintronics is an emerging research field of electronics: spintronics devices are based on a spin control of electronics, or on an electrical and optical control of spin or magnetism. This review presents selected themes of semiconductor spintronics, introducing important concepts in spin transport, spin injection, Silsbee-Johnson spin-charge coupling, and spindependent tunneling, as well as spin relaxation and spin dynamics. The most fundamental spin-dependent nteraction in nonmagnetic semiconductors is spin-orbit coupling. Depending on the crystal symmetries of the material, as well as on the structural properties of semiconductor based heterostructures, the spin-orbit coupling takes on different functional forms, giving a nice playground of effective spin-orbit Hamiltonians. The effective Hamiltonians for the most relevant classes of materials and heterostructures are derived here from realistic electronic band structure descriptions. Most semiconductor device systems are still theoretical concepts, waiting for experimental demonstrations. A review of selected proposed, and a few demonstrated devices is presented, with detailed description of two important classes: magnetic resonant tunnel structures and bipolar magnetic diodes and transistors. In most cases the presentation is of tutorial style, introducing the essential theoretical formalism at an accessible level, with case-study-like illustrations of actual experimental results, as well as with brief reviews of relevant recent achievements in the field.Comment: tutorial review; 342 pages, 132 figure

Approaches to accident investigation by investigators from different cultures

Cultural characteristics play a significant part in aviation (Helmreich & Merritt, 1998). The collective nature of Chinese society is consistent with broad, contextual view of the world and their belief that events are highly complex and determined by many factors. On the other side, the individualistic nature of Western society seems consistent with the focus on particular objects in isolation from their context and with Westerners’ belief that they can know the rules governing objects and therefore can control the objects’ behavior (Nisbett, 2003). Westerners have a strong interest in categorization, which helps them to know what rules to apply to the objects, and formal logic plays a role in problem solving. Chinese attend to objects in their broad context. The world seems more complex to Chinese than to Westerners, and understanding events always requires consideration of many factors that operate in relation to one another in no simple way. From the I-Ching (ancient Chinese philosophical book), ‘for misery, happiness is leaning against it; for happiness, misery is hiding in it. Who knows whether it is misery or happiness? There is no certainty. The righteous suddenly becomes the vicious; the good suddenly becomes the bad’. Chinese is less concerned with finding the truth than with finding the harmony way to live in the world. As the result, Chinese failure to develop science can be attributed in part to lack of curiosity to the true, but the absence of a concept of nature would have blocked the development of science in any case

Do cultural characteristics affect investigation?

Separating the people from the problem assumes an individualist value set underlying the Western approach to investigation. In collectivist cultures, where relationships prevail over tasks, this is an almost impossible demand. Effective investigation for aviation accidents within different cultural contexts demands insight into the range of cultural values to be expected among partners from other countries, in addition to an awareness of the investigator’s own culturally determined values. Effective international investigations also demand language and communication skills to guarantee that the messages sent to the other professional investigators from different cultures with different approaches to accident investigation will be understood in the way they were meant to be. The global interaction between different cultures involves sharing the values of all partners. It is important to know more about the similarities and differences in culture-influenced accident investigation philosophies, e.g., when European and Asian culture collaborate together. The cognitive orientation and mechanisms of Eastern and Western cultures are sufficiently different that they may draw completely different inferences from the same set of data (as in this case), especially in the case where human factors are concerned. The best approach may be to try to understand the events in the accident from the viewpoint of the culture of the pilots/airline involved in the accident and not from the cultural viewpoint of the investigator. This way there might be a better chance that culturally congruent remedial actions can be proposed. However, by better understanding these cultural differences it seems highly likely that they can only serve to complement and enrich each other

International cooperation and challenges: Understanding cross-cultural issues in the processes of accident investigation

The idea that national cultural characteristics play a part in aviation safety had been suggested by Helmreich & Merritt (1998). This research involved around 45 aviation accident investigators from different cultural backgrounds and investigated attribution of causal factors in the Ueberlingen accident report through the application of the Human Factors Analysis and Classification System (Wiegmann & Shappell, 2003). Hofstede’s (1991 & 2001) cultural dimensions draw a clear picture of the attributable patterns of human errors based on cultural differences. As a result it is necessary to develop a better understanding of the differences in attribution of accident causes and contributory factors across cultures to promote both aviation safety and international cooperation for accident investigation will be achieved. Furthermore, when suggesting safety enhancements resulting from accident investigations it needs to be noted that the same remedy may not work in different cultures. Remedial actions must be 'culturally congruent'. This process starts with understanding the cultural factors at work in the accident investigation process itself