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翻訳と辞書　辞書検索 [ 開発暫定版 ] スポンサード リンク Josephson junctions ： ウィキペディア英語版 Josephson effect The Josephson effect is the phenomenon of supercurrent—i.e. a current that flows indefinitely long without any voltage applied—across a device known as a Josephson junction (JJ), which consists of two superconductors coupled by a weak link. The weak link can consist of a thin insulating barrier (known as a superconductor–insulator–superconductor junction, or S-I-S), a short section of non-superconducting metal (S-N-S), or a physical constriction that weakens the superconductivity at the point of contact (S-s-S). The Josephson effect is an example of a macroscopic quantum phenomenon. It is named after the British physicist Brian David Josephson, who predicted in 1962 the mathematical relationships for the current and voltage across the weak link.〔Josephson, B. D., "Possible new effects in superconductive tunnelling," ''Physics Letters'' 1, 251 (1962) 〕 The DC Josephson effect had been seen in experiments prior to 1962, but had been attributed to "super-shorts" or breaches in the insulating barrier leading to the direct conduction of electrons between the superconductors. The first paper to claim the discovery of Josephson's effect, and to make the requisite experimental checks, was that of Philip Anderson and John Rowell. These authors were awarded patents on the effects that were never enforced, but never challenged. Before Josephson's prediction, it was only known that normal (i.e. non-superconducting) electrons can flow through an insulating barrier, by means of quantum tunneling. Josephson was the first to predict the tunneling of superconducting Cooper pairs. For this work, Josephson received the Nobel prize in physics in 1973.〔(The Nobel prize in physics 1973 ), accessed 8-18-11〕 Josephson junctions have important applications in quantum-mechanical circuits, such as SQUIDs, superconducting qubits, and RSFQ digital electronics. The NIST standard for one volt is achieved by an array of 19,000 Josephson junctions in series.〔Steven Strogatz, ''Sync: The Emerging Science of Spontaneous Order'', Hyperion, 2003. 〕 A Dayem bridge is a thin-film variant of the Josephson junction in which the weak link consists of a superconducting wire with dimensions on the scale of a few micrometres or less.〔Anderson, P. W., and Dayem, A. H., "Radio-frequency effects in superconducting thin film bridges," ''Physical Review Letters'' 13, 195 (1964), 〕 ==The effect== The basic equations governing the dynamics of the Josephson effect are :$U(t)\; =\; \backslash frac\; \backslash frac$ (superconducting phase evolution equation) :$\backslash frac$ is the magnetic flux quantum, the inverse of which is the Josephson constant. The three main effects predicted by Josephson follow from these relations: ;The DC Josephson effect: The DC Josephson effect is a direct current crossing the insulator in the absence of any external electromagnetic field, owing to tunneling. This DC Josephson current is proportional to the sine of the phase difference across the insulator, and may take values between $\backslash scriptstyle\; -I\_c$ and $\backslash scriptstyle\; I\_c$. ;The AC Josephson effect: With a fixed voltage $\backslash scriptstyle\; U\_$ across the junctions, the phase will vary linearly with time and the current will be an AC current with amplitude $\backslash scriptstyle\; I\_c$ and frequency $\backslash frac\; U\_$. The complete expression for the current drive $I\_\backslash text$ becomes $I\_\backslash text\; \backslash ;=\backslash ;\; C\_J\; \backslash frac\; \backslash ,+\backslash ,\; I\_J\; \backslash sin\; \backslash phi\; \backslash ,+\backslash ,\; \backslash frac$. This means a Josephson junction can act as a perfect voltage-to-frequency converter. ;The inverse AC Josephson effect: If the phase takes the form $\backslash scriptstyle\; \backslash phi\; (t)\; \backslash ;=\backslash ;\; \backslash phi\_0\; \backslash ,+\backslash ,\; n\; \backslash omega\; t\; \backslash ,+\backslash ,\; a\; \backslash sin(\; \backslash omega\; t)$, the voltage and current will be :$U(t)\; =\; \backslash frac\; \backslash omega\; (\; n\; +\; a\; \backslash cos(\; \backslash omega\; t)\; ),\; \backslash \; \backslash \; \backslash \; I(t)\; =\; I\_c\; \backslash sum\_^\backslash infty\; J\_m\; (a)\; \backslash sin\; (\backslash phi\_0\; +\; (n\; +\; m)\; \backslash omega\; t).$ The DC components will then be :$U\_\; =\; n\; \backslash frac\; \backslash omega,\; \backslash \; \backslash \; \backslash \; I(t)\; =\; I\_c\; J\_\; (a)\; \backslash sin\; \backslash phi\_0.$ Hence, for distinct AC voltages, the junction may carry a DC current and the junction acts like a perfect frequency-to-voltage converter. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Josephson effect」の詳細全文を読む スポンサード リンク 翻訳と辞書 : 翻訳のためのインターネットリソース Copyright(C) kotoba.ne.jp 1997-2016. All Rights Reserved.