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

Discovery or Invention: Modern Interpretations of Zhang Xuecheng

Zhang Xuecheng was an ordinary scholar in eighteenth-century China. But in modern times he was recognized as an extraordinary historian. His remark that "the Six Classics are all history" was especially praised as a remarkable breakthrough or distinct paradigm. This study, however, argues that the rediscovery of Zhang was in effect a modern invention. "The Six Classics are all history" is actually quite an old concept. At least from the sixteenth-century on, Wang Yangming had already set a precedent for Zhang, whose version of the dictum was quite similar to his predecessors as well as contemporaries. Zhang filled in little, if any, new wine in the old bottle. He found no new meaning in history, as he believed the so-called Dao, or Way, contained in the Six Classics was as eternal as the sun and the moon and applied to hundreds of generations to come. He had no intention of turning history against the Classics, or of replacing the Classics with history, as modern scholars have claimed. His view of history was well within the bounds of Confucian historiography. Zhang attached a great deal of importance to history, but he was not unique in this regard. His historiography rested almost totally on the laurels of orthodox Confucianism. He criticized Dai Zhen, but his criticism was generally based on moral grounds and it seems to have little epistemological significance. Zhang Xuecheng emphasized the importance of history to serve statecraft (jingshi), but this view, too, was scarcely original. In this regard, he was more a successor than an innovator. He remained a rather old-fashioned scholar in the eighteenth century. The rediscovery of Zhang in modern times actually reflects modern scholars' concerns. They read their own ideas into Zhang Xuecheng's writings. Zhang never considered the Classics or history as mere historical materials as modern historians do. Nor did Zheng try to secularize the Classics and history, which might have constituted a major breakthrough in the conception of historiography. A secularized Zhang was thus the invention of modern scholars. In addition, only modern scholars, like Collingwood and Qian Zhongshu, who consider the past dead, feel duty-bound to breathe new life into this moribund history. There are no striking similarities, as a modern scholar claims, between eighteenth-century Zhang and twentieth-century Collingwood. This study is as much interested in exposing misrepresentations as in revealing the modern concerns that helped invent Zhang. These concerns, in fact, reflect the dramatic changes of modern Chinese historiography