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

研究了SPM法制备的多壁碳纳米管场效应晶体管（MWNT FET）器件中与单壁碳纳米管（SWNT）纳米接触的低温磁电阻效应。在单壁碳纳米管的情况下，表面自旋的圆化配置预计将产生纳米尺度的运输效果，以及Rashba型潜力。这种效应会影响碳纳米管（CNT）中与电子波量子相干性相关的弱局域化MR行为。在过去的几年中，我们已经报道了AAS型振荡的MR在一个类似的纳米级接触形成的交叉的两个多壁碳纳米管。然而，在这一年中，反本地化型振荡已被观察到在一个单壁碳纳米管和多壁碳纳米管之间的混合接触，尽管没有碳的自旋轨道相互作用。在我们的项目中，两种类型的混合设备已经准备好我们的MR测量。这些是位于MWNT电流路径下方的SWNT束的短棒或单环。用He-3低温恒温器进行了低温MR测量。随着源极-漏极偏压的改变，在相同的混合CNT器件中可以观察到负和/或正MR峰。在没有底层SWNT的情况下，在一根MWNT丝的低温MR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的MWNT的整个区域上传播。因此，结果表明，单壁碳纳米管的量子相干性的影响很大。这两种碳纳米管中的干涉行为可以作为分析单壁碳纳米管小自旋浓度体系中纳米尺度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.