Control of spin motion in DOS-controlled single-wailed carbon nanotubes

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The purpose of this study is (1) stable control of density of states (DOS) in single-walled carbon nanotubes (SWNTs) in order to control injected carriers, (2) injection of polarized spins into DOS-controlled SWNTs. In order to achieve these two purposes, we have set 3 important milestones, that is, (a) increase of carrier injection efficiency in SWNT-based field effect transistors, (b) band engineering of SWNTs as a channel layer in FETs by carrier doping (c) spin injection into such SWNTs from ferromagnetic electrodes. Concerning the milestone (a) and (b), we have succeeded in fabricating SWNT-FETs with high performance and also polarity controlled SWNT-FETs using Tetracyano-p-quinodimethane (TCNQ) and polyethireneimine. Concerning the milestone (c), first we fabricated single-electron transistors using SWNT and estimated scattering length of injected carriers (electron and hole) to be 200-300 nm. Next we replaced electrodes from non-magnet to ferromagnet in order to achieve spin injection. In addition, we newly introduced a non-local 4-terminal magnetoresistance measurement method for obtaining reliable results. As a result, we have observed hysteresis in resistance in SWNT spin valve with 4 electrodes at 3.8 K. The spin coherent length was estimated to be about 90 nm.