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首页> 外文期刊>Nature >Quantum supercurrent transistors in carbon nanotubes.
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Quantum supercurrent transistors in carbon nanotubes.

机译：碳纳米管中的量子超电流晶体管。

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摘要

Electronic transport through nanostructures is greatly affected by the presence of superconducting leads. If the interface between the nanostructure and the superconductors is sufficiently transparent, a dissipationless current (supercurrent) can flow through the device owing to the Josephson effect. A Josephson coupling, as measured by the zero-resistance supercurrent, has been obtained using tunnel barriers, superconducting constrictions, normal metals and semiconductors. The coupling mechanisms vary from tunnelling to Andreev reflection. The latter process has hitherto been observed only in normal-type systems with a continuous density of electronic states. Here we investigate a supercurrent flowing through a discrete density of states-that is, the quantized single particle energy states of a quantum dot, or 'artificial atom', placed between superconducting electrodes. For this purpose, we exploit the quantum properties of finite-sized carbon nanotubes. By means of a gate electrode, successive discrete energy states are tuned on- and off-resonance with the Fermi energy in the superconducting leads, resulting in a periodic modulation of the critical current and a non-trivial correlation between the conductance in the normal state and the supercurrent. We find, in good agreement with existing theory, that the product of the critical current and the normal state resistance becomes an oscillating function, in contrast to being constant as in previously explored regimes.
机译：通过纳米结构的电子传输在很大程度上受到超导引线的影响。如果纳米结构和超导体之间的界面足够透明，则由于约瑟夫森效应，无耗散电流（超电流）可以流经器件。使用隧道势垒，超导缩颈，普通金属和半导体已经获得了通过零电阻超电流测量的约瑟夫森耦合。耦合机制从隧穿到Andreev反射不等。迄今为止，仅在具有连续电子态密度的普通型系统中才观察到后一种过程。在这里，我们研究流过离散状态密度（即量子点或“人造原子”的量子化单粒子能量状态）的超电流，该量子点位于“超导”电极之间。为此，我们利用了有限尺寸的碳纳米管的量子特性。借助栅电极，连续的离散能量状态与超导导线中的费米能量一起进行开和关谐振的调谐，从而导致临界电流的周期性调制以及正常状态下电导之间的平凡关系和超电流。与现有理论完全一致，我们发现临界电流和正常状态电阻的乘积成为振荡函数，与之前探索的机制中的常数相反。

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