Material and functional study for the spin manipulation

我们探索了在强磁场下操纵单壁碳纳米管（SWCNA）量子点电子自旋和GaAs/AlGaAs异质结二维电子气孤立边缘态的可能性。在这两种情况下，可以预期具有明确定义的自旋方向的束缚态。我们发现单壁碳纳米管量子点是单自旋产生和操纵的有希望的构建块。单量子点是通过在单个单壁碳纳米管顶部沉积金属接触来简单地制造的，并且接触之间的单壁碳纳米管表现为单量子点。实验中测得的能级间距与接触之间的差距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，库仑振荡的周期为两个a 关于我们 观察到四个电子。前者是由于单壁碳纳米管的能带简并以及自旋简并引起的。后者出现时，由于材料的不完善，带简并被解除，自旋简并仍然存在。这些观察表明，单壁碳纳米管量子点具有四电子或二电子壳层结构。观察到零维受限态，当施加磁场时，零维受限态分裂为两个漂白态，这是塞曼分裂的明显证据。当壳层中存在两个电子时，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。这两种状态在零磁场下具有不同的能量。门脉冲测量表明，塞曼能级的能量弛豫时间大于1微秒，实验的重要意义是，即使量子点中有许多电子，也能观察到壳层结构，这与半导体量子点中只有少数电子才能观察到壳层结构形成了鲜明的对比。这是由于零维能级间距远大于SWCNT量子点中的电子-电子相互作用能，这意味着可以通过将一个电子放入壳层中来产生单自旋。我们曾尝试用电子自旋共振（ESR）技术在10 ~ 100 GHz的频率范围内对单自旋进行相干操纵，但没有成功。电磁波和自旋之间的耦合越强，就越有必要。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