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中文摘要：
利用量子波导理论研究三臂环中的持续电流。结果表明,输运电流存在时,不含磁场且上、下臂等长的三臂环中仍可以有持续电流出现,而且上臂和下臂中的持续电流是相同的。三臂环的各臂长不等时,三个臂中的持续电流各不相同。我们还发现,即使三臂环和单环的上、下臂比值一样,两个环中的持续电流也明显不同。
英文摘要：
In recent years, many works have been devoted to the study of the mesoscopic systems, because the electronic transport property in mesoscopic systems is not only a basic theoretical topic but also could benefit the design of useful electronic devices. Research on these systems revealed many novel phenomena. These phenomena, which usually appear in mesoscopic systems, are called mesoscopic phenomena. One of the mesoscopic phenomena is the persistent current flowing in a mesoscopic ring threaded by a magnetic flux. Experimental and theoretical research has shown that a magnetic flux which threads an isolated ring of mesoscopic dimensions creates persistent current. Moreover, it has been theoretically shown that in such a system serf-sustaining current can still run even if the external flux is switched off. General quantum-mechanical principles require that the wave functions, eigenvalues, and hence all observable quantities should be periodic in the magnetic flux φ threading the loop with a period φ0 （φ0 = hc/e being the flux quantum）. It is well known that the magnetic flux destroys the time-reversal symmetry and, as a consequence, the degeneracy of the states carrying current clockwise and anticlockwise is lifted. Since the discovery of the persistent current, there have been many studies on the single ring, coupled ring, and multiple-arm ring structures. Studies show us that in the presence of a transport current, the persistent current can flow in a ring, even in the absence of a magnetic field. The purpose of this paper is to study persistent currents in the triple-arm ring coupled to two external leads by quantum waveguide theory. It is found that in the presence of a transport current, the persistent currents can flow in a triple-arm ring, even if the magnetic flux is absent and the lengths of the upper and the ower arms are equal. With different lengths of the three arms, the persistent currents in the three arms are different. Beside, the persistent currents in the triple-arm ring and the single ri
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