Material and functional study for the spin manipulation

我们探索了在高磁场下操纵单壁碳纳米管（SWCNA）中量子点的选择自旋和GaAs/AlGaAs异质结构中二维电子气体中的孤立边缘态的可能性。在这两种情况下，可以预期具有明确自旋方向的束缚态。我们发现SWCNT量子点是单自旋产生和操纵的有希望的构建块。单量子点是简单地通过在单个SWCNT上沉积金属触点来制造的，触点之间的SWCNT表现为单个量子点。实验中测量的能级间距与具有接触间隙长度的简单一维模型一致，这一事实证实了这一点。在毫开尔文温度下进行了单电子输运测量，以研究量子点的人工原子性质。在低温下，库仑振荡的周期为2 a。前者来源于swcnts的能带简并和自旋简并。后者是由于材料的缺陷导致能带简并被解除，而自旋简并仍然存在。这些观察结果表明，swcnts量子点具有四个或两个电子壳层结构。通过测量具有较大源漏偏置电压的库仑峰，进行了激发光谱分析。零维受限态在磁场作用下分裂为两个白化态，这是塞曼分裂的明显证据。当壳层中存在两个选择时，观察到相互作用的双电子系统的量子态，即单重态和三重态。这两种状态在磁场为零时能量不同。门脉冲测量结果表明，塞曼能级的能量弛豫时间大于1微秒。该实验的重要意义在于，即使在量子点中有许多电子，也可以观察到壳层结构，这与半导体量子点只有在点中有很少电子时才能观察到壳层结构形成鲜明对比。这是由于零维能级间距远远大于SWCNT量子点中的电子-电子相互作用能，这意味着将一个电子放入壳层中可以产生单自旋。我们曾尝试用电子自旋共振（ESR）技术在10ghz ~ 100GHz频率范围内对单自旋进行相干操纵，但没有成功。操纵它。自旋与电磁波之间更强的耦合是必要的。少

We have explored possibilities of manipulation of election spins in quantum dots in single wall-carbon nanotubes (SWCNA) and isolated edge states in a two dimensional electron gas in GaAs/AlGaAs heterostructures under the high magnetic fields. In both cases, bound states with well defined spin direction can be expected. We found that the SWCNT quantum dots are promising building blocks for single spin generation and manipulation.The single quantum dot was fabricated simply by depositing metallic contacts on top of an individual SWCNT, and the SWCNT between the contacts behaves as a single quantum dots. This is confirmed by the fact that the energy level spacing measured in experiments agreed with a simple one-dimensional model with a length of the gap between the contacts. Single electron transport measurements have been carried out at milli-Kelvin temperatures to investigate the artificial atom nature of the quantum dot. At low temperatures, Coulomb oscillations with a period of two a … More nd four electrons are observed. The former arises from the band degeneracy of the SWCNT in addition the spin degeneracy. The latter appears when the band degeneracy is lifted due to imperfection of the material, and the spin degeneracy remains. These observation indicates that the SWCNT quantum dot show four or two electron shell structures.The excitation spectroscopy has been carried out by measuring a Coulomb peak with a large source drain bias voltage. Zero-dimensional confined states are observed, which split into two blanched as the magnetic field is applied, a clear evidence of the Zeeman splitting. When two elections are existing in a shell, the quantum states of the interacting two-electron system, which are the singlet and triplet states, observed. The two states have a different energy at a zero magnetic field. The gate-pulse measurements revealed that the energy relaxation time in the Zeeman levels were more than lmicro second.The important implication of the experiments is that the shell structures are observable even many electrons in a quantum dot which is in a striking contrast to semiconductor quantum dots where shell structures are only observable with few electrons in a dot. This is due to the fact that the zero-dimensional level spacing is much larger than electron-electron interaction energy in the SWCNT quantum dot This means that single spin can be generated by putting one electron in a shell. We have tried to coherently manipulate the single spin by using the Electron Spin Resonance (ESR) technique in frequencies ranging from 10 GHz to 100GHz, but the we did not succeed in. manipulating it. The stronger coupling between the spin and the electromagnetic wave is necessary. Less