臺灣博碩士論文加值系統

在本論文中，我們研究吸附雙原子分子的轉動能態和量子點的物理性質。在第一部份中，我們考慮高強度雷射場照射在受到角錐位能井局限的吸附極性分子上，藉由改變位能井的禁制角度，我們觀察分子從自由轉動過渡到禁制轉動的行為。同時，我們也進一步探討耦合自由與吸附分子的轉動能態，發現其分子偏向與單一吸附分子的偏向有相當不同的差異性，原因是來自於分子間偶極作用的影響。此外，我們也計算了von Neumann熵來定義耦合分子系統的糾纏程度，結果發現糾纏會受到分子間距離、雷射脈衝強度與數目以及局限效應的影響。
在第二部份中，我們探討量子點系統的自旋弛豫與電子傳輸的現象。當量子點被製備在半導體平板內，我們發現由於聲子與自旋軌道交互作用的影響，自旋弛豫會顯現出類似共振腔的行為；另外，為了研究聲子在電子傳輸的效應，我們進一步考慮雙量子點元件處在一個單一聲子的環境中，結果顯示傳輸行為強烈地受到庫倫或是聲子場的影響。最後，我們也研究雙量子點在外加場作用下的電子傳輸現象，由於電子能態與外加場交互作用，我們發現電流大小會受到提升或是壓抑。

In this dissertation, we study the rotational states of adsorbed diatomic molecules and some physical properties of quantum dots. In part I, an adsorbed dipole molecule confined by a conical well is subject to strong laser fields. The crossover from field-free to hindered rotation motion is observed by varying the hindering angle. Moreover, the rotational states of coupled free and adsorbed molecules with dipolar interaction are further studied. It is shown that the orientation is significantly different from that of an isolated one due to the dipole-dipole interaction. In addition, the von Neumann entropy is calculated to characterize the degree of entanglement. It is also found that the entanglement can be influenced by the inter-molecule distance, the strength and number of laser pulses, and the confinement effect.
In part II, we investigate the spin relaxation and electron transport in quantum dot systems. When a quantum dot is embedded in a semiconductor slab, the spin relaxation rate shows peculiar behaviors due to the confined phonons. Second, to observe the phonon effect on the transport, we have also considered a double-dot device embedded in a single phonon environment. It is shown that the transport behavior is deeply influenced by the Coulomb or phonon field. Finally, the transport of a double-dot device irradiated by an external field is considered. The enhanced or suppressed current is found due to the interplay between the energy states and external field.

LIST OF FIGURES . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . .xiv
1 INTRODUCTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1
2 INTRODUCTION TO PART I . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . .3
3 AN ADSORBED DIPOLE MOLECULE IN LASER FIELDS . . . . . . . . . . . . . .8
3.1 Model of an adsorbedmolecule . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . 9
3.2 Connection between theory and experiment . . . . . . . . . . . . . . . . . . . .. . . . . 12
3.3 An adsorbed molecule in a strong laser field . . . . . . . . . . . . . . . . . . . . . . . . 14
3.4 Results and discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . 16
4 COUPLED FREE MOLECULES IN LASER FIELDS . . . . . . . . . . . . . . . .25
4.1 Model of two coupled free molecules in a strong laser pulse . . . . . . . . . . . . . . 26
4.2 Entanglement of two coupled freemolecules . . . . . . . . . . . . . . . . . . . . . . . . . 28
4.3 Results and discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
5 COUPLED ADSORBED MOLECULES IN LASER FIELDS . . . . . . . . . . . . .46
5.1 Single adsorbedmolecule in a strong laser pulse . . . . . . . . . . . . . . . . . . . . . . 47
5.2 Two coupled adsorbedmolecules in a strong laser pulse . . . . . . . . . . . . . . . . . 51
6 SUMMARY AND FUTURE WORK . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .61
7 INTRODUCTION TO PART II . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .64
8 SPIN RELAXATION IN A GAAS QUANTUM DOT EMBEDDED INSIDE
A SUSPENDED PHONON CAVITY . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .69
8.1 Model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . 71
8.1.1 Single particle in a quantumdot . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . 71
8.1.2 Confined phonon in a semiconductor slab . . . . . . . . . . . . . . . . . . . .. . . . . 73
8.1.3 Electron-phonon coupling and scattering rate . . . . . . . . . . . . . . . . . .. . . . . 75
8.2 Results and discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . 76
9 ELECTRON TRANSPORT THROUGH A DOUBLED QUANTUM DOT
SYSTEM WITH SINGLE PHONON MODE . . . . . . . . . . . . . . . . . . . . . . . . . . . .86
9.1 Model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 88
9.2 Results and discussion . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . .. . . 93
10 ELECTRON TRANSPORT THROUGH A DRIVEN THREE-LEVEL DOUBLE DOT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .101
10.1 Model . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . .. . . . . . ... . . 102
10.2 Results and discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 106
11 SUMMARY AND FUTURE WORK . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .116

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