| Project/Area Number |
14076218
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| Research Category |
Grant-in-Aid for Scientific Research on Priority Areas
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| Allocation Type | Single-year Grants |
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| Review Section |
Science and Engineering
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| Research Institution | The Institute of Physical Chemical Research (RIKEN) |
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Principal Investigator |
ISHIBASHI Koji Advanced Device Lab. RIKEN, Chief Scientist, 石橋極微デバイス工学研究室, 主任研究員 (30211048)
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| Project Period (FY) |
2002 – 2005
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| Project Status |
Completed (Fiscal Year 2005)
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| Budget Amount *help |
¥19,800,000 (Direct Cost: ¥19,800,000)
Fiscal Year 2005: ¥5,400,000 (Direct Cost: ¥5,400,000)
Fiscal Year 2004: ¥5,500,000 (Direct Cost: ¥5,500,000)
Fiscal Year 2003: ¥5,300,000 (Direct Cost: ¥5,300,000)
Fiscal Year 2002: ¥3,600,000 (Direct Cost: ¥3,600,000)
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| Keywords | Carbon nanotube / Artificial atom / Quantum dot / Zeeman effect / Single electron transport / Interacting two-electron system / 量子ビット / 単電子トランジスタ / スピン量子操作 / スピン緩和時間 / ゼーマン分裂 / GaAs / AlGaAs2次元電子ガス / アンチドット / 量子ホール効果 / エッジ状態 / 単電子輸送現象 / 電子殻構造 / スピン操作 / 電子数の偶奇性効果 / クーロンブロッケード |
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| Research Abstract |
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
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