Electron states in semiconductor quantum structures

Abstract

The theoretical studies on electronic states and transport properties in quantum structures fabricated in semiconductors have been carried out to clarify the effects of electron correlation and disorder on electronic states. By the observation of the fractional quantum Hall effect, it was found that the electron correlation played an important role in the two dimensional electron systems in strong magnetic fields. The numerical calculations were performed for many-body states in two parallel layers of two dimensional systems, and the ground state was calculated using exact diagonalization technique for rectangular systems with the periodic boundary condition in the two directions. The possibility of a new state in which electrons formed pairs with the relative angular momentum zero has been suggested by the results. From the remarkable effects of the electron interaction in a quantum dot observed as the Coulomb blockade oscillations, it was found that the electron correlation in a quantum dot also important. Effects of disorder were discussed in connection with the transport through quantum structure in the quite clean systems. The exact numerical simulation for the conductance fluctuations for the system near the ballistic transport regime was performed.

電子状態に及ぼす電子相関および無秩序の効果を明らかにするために、半導体中に組込まれた量子構造の電子状態および輸送特性を理論的に研究した。分数量子ホール効果の観察から、電子相関が強磁場における2次元電子系で重要な役割を果たすことが分かった。2次元系の2平行層における多体状態について数値計算を行うとともに、2方向に周期的境界条件を持つ矩形系について、厳密対角化手法を用いて基底状態を計算した。計算結果は電子が相対角運動量ゼロの対を形成する新規状態の可能性を示唆した。クーロン封鎖振動として観察した量子ドットの電子相互作用の顕著な効果から、量子ドットにおける電子相関もまた重要であることが分かった。無秩序の効果を完全清浄系の量子構造を通る輸送との関連で論じた。弾道型伝導領域近くの系のコンダクタンスのゆらぎについての厳密数値シミュレーション研究を行った。