微共振腔激子偏振子之超導電流研究

Abstract

此計畫主要研究激子-偏振子 (exciton-polariton)電傳導特性的理論及其應用。激子-偏振子是由光子 (photon)與激子 (exciton)所組成的準粒子 (quasiparticle)。因質量極輕，激子-偏振子可在室溫下產生波愛凝結 (Bose-Einstein condensation)。此高相變溫度(critical temperature)，可能應用於高溫超導體元件設計。然由於實驗技術與理論預測的困難，激子-偏振子的超導電流特性多未被開發。在此我們提案探討兩系統中的激子-偏振子超導電流。 在第一提案中我們研究微空腔(microcavity)中半導體雙層(semiconductor bilayer) 的激子-偏振子超導電流。因激子-偏振子超導電流須以費米理論描述，我們將針對該系統開發平衡與非平衡態的費米模型，並進步提議以縱向電流來開關激子-偏振子超導電流裝置。第二提案中，我們研究偶極子(dipolariton)之電導性質。偶極子是由光子與直接，間接兩種激子組成，其中的間接激子使偶極子產生偶極矩。經由調變直接與間接激子的共振，可改變偶極矩之強弱。我們將發展費米理論來描述偶極子之電傳特性並探討其豐富的相圖。 我們預期經由此二提案深入理解激子-偏振子超導電流。此研究不單將對基礎物理科學有重大影響。在應用上也將裨益高溫超導體元件之設計。

This research proposal focuses on the theoretical understanding of electrical transport of exciton-polariton superfluid and further suggests potential applications. An exciton-polariton is a bosonic quasiparticle composed of an exciton and a photon. Its extremely light mass enables the Bose-Einstein condensation to happen at temperatures as high as room temperature. This high critical temperature shed light on high temperature supercurrent devices. However, electrical supercurrent in such system is still underexplored because of the challenges in both experimental and theoretical aspects. Inspired by the recent experimental breakthrough, we propose to study two possible schemes of electrical transport in this exciton-polariton superfluid. In the first scheme, we will investigate the electrical supercurrent of exciton-polariton in the semiconductor bilayers that are embedded in a microcavity. Fermionic models -- that capture the essential physics of bilayers excitonic supercurrent -- will be developed in both quasi-equilibrium and non-equilibrium regimes. Moreover we will propose an efficient switch of such supercurrent that uses a tunneling bias orders smaller than the excitonic gap. In the second scheme, we will study the electrical transport of dipolariton, a new quasiparticle that comprises photon, direct- and indirect-exciton. Its indirect-exciton component, in particular, gives rise to dipole moment. The magnitude of this dipole moment is tuned by a gate voltage, which modifies the resonance between the direct- and indirect-exciton. We will develop also a fermionic theory to describe the electrical transport and explore the abundant phase diagram originated from its complex constituents. We expect to gain deep understanding over the supercurrent transport of exciton-polariton through these two topics. The study will be significant for fundamental science due to the multi-component nature of exciton-polariton. Moreover, it can shed light on high temperature supercurrent devices.