Coherent Control of Quantum Phase in Single- and Multi-Wall Carbon Nanotubes Combined System

研究了多壁碳纳米管（MWNT） FET器件与单壁碳纳米管（SWNT）纳米级接触时的低温磁阻（MR）。在SWNT的情况下，表面自旋的舍入配置预计会产生纳米级输运效应以及Rashba型势。这种效应会影响碳纳米管（CNT）中电子波量子相干性的弱局部化磁流变行为。在过去的几年里，我们已经报道了由两个mwnt交叉形成的类似纳米级接触在MR中的AAS型振荡。然而，在今年，尽管没有碳的自旋轨道相互作用，但在SWNT和MWNT之间的杂化接触中观察到反局域化型振荡。在我们的项目中，为我们的MR测量准备了两种混合装置。它们是位于MWNT当前路径下方的SWNT束的短条或单个环。使用He-3低温恒温器进行了低温磁共振测量。随着源漏偏置的变化，在相同的混合碳纳米管器件中可以观察到负和/或正的MR峰。在没有底层SWNT的情况下，在一根MWNT导线的低温磁流变中观察到两种或三种AB振荡。电子的相干性在电压引线触点之间扩散到MWNT的整个区域。因此，研究结果表明，潜在的SWNT对MWNT的量子相干特性有很大的影响。这两种碳纳米管之间的干扰行为可以作为分析小自旋浓度体系中纳米级弱局域化的有力工具。

The low temperature magnetoresistance (MR) associated with the nano-scale contact to a single-walled carbon nano-tube (SWNT), has been studied for multi-walled carbon nano-tube (MWNT) FET devices fabricated by SPM-manipulation. In a case of SWNT, the rounding configuration of the surface spin is expected to produce a nano-scale effect for the transport as well as a Rashba type potential. Such an effect should influence the weak localization MR behavior related to quantum coherence of the electron waves in the carbon nano-tube (CNT). In previous years, we have reported AAS type oscillations in the MR at a similar nano-scale contact formed by the crossing of two MWNTs. However, in this year, anti-localization type oscillations have been observed in a hybrid contact between a SWNT and a MWNT in spite of absence of spin-orbit interaction for carbon. In our project, two kinds of the hybrid devices have been prepared for our MR measurements. These are a short bar or a single ring of a SWNT bundle that lies beneath the current path of a MWNT. Low temperature MR measurements have been performed using He-3 cryostat. With change of the source-drain bias, a negative and/or positive MR peak can be observed in the same hybrid CNT device. In the case where there is no underlying SWNT, two or three kinds of AB oscillations have been observed in the low temperature MR of one MWNT wire. The coherence of the electron spreads over the whole region of the MWNT between the voltage lead contacts. Therefore, the results show that underlying SWNT is strongly affected to the quantum coherent property of MWNT. Such interference behaviors in the both CNTs should be utilized as a powerful tool on the analyzing of nano-scale weak localization in a small spin concentration system of the SWNT.