單電子系統中的電子穿隧事件

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题名:	單電子系統中的電子穿隧事件
作者:	戴伯誠;Tai,Pochen
贡献者:	物理學系
关键词:	混合式單電子箱;單電子晶體;電流標準;共同穿隧;古柏對分裂;hybrid single-electron box;single-electron transistor;current standard;cotunneling;Cooper pair splitting
日期:	2014-10-29
上传时间:	2014-11-24 15:21:42 (UTC+8)
出版者:	國立中央大學
摘要:	單電子系統之電子分佈狀態(charge state)受庫倫阻絕效應(Coulomb blockade)影響，系統中電子數目無法任意增減，需提供充電能量(charging energy)才可使系統淨電荷數改變。由於此特性，單電子元件可用於研究單一電子之穿隧事件，如古柏對分裂(cooper pair splitting)。本實驗製作由超導金屬(S)及一般金屬(N)構成之混合式單電子箱(hybrid single-electron box)。此電子箱是由三金屬島組成之獨立導體(NISIN-island)，分別以鋁與銅做為超導金屬島與一般金屬島，兩者透過穿隧屏障(I)相接。各金屬島皆與一鄰近電極耦合，用以調控金屬島偏壓，並改變系統自由能，使電子於各金屬島間穿隧。將兩個單電子電晶體與三金屬島系統中兩金屬島耦合，用以偵測電子箱中的電子分佈狀態，進而觀測在NIS介面的電子穿隧事件。實驗上取得之數據能提供我們瞭解系統於不同偏壓條件有穿隧事件發生，但無法辨認其種類，因此我們透過靜電學分析，模擬實驗系統，繪製電子狀態分佈圖(stability diagrams)，再與實驗觀測數據相比較，以判斷電子穿隧事件之種類。此工作可用於研究單電子元件製作的電流標準(current standard)中，發生錯誤率的主要成因－共同穿隧(cotunneling)之發生率。相似的混合式單電子箱，亦可研究古柏對分裂。各章節概述如下： Chapter 1: 單電子元件之工作原理分析及其應用。而本實驗主要使用之元件為混合式單電子箱及混合式單電子電晶體。 Chapter 2: 本實驗使用之製程技術及元件製作材料、參數及方法。 Chapter 3: 單電子元件的電子分佈狀態模擬，並與實驗結果相比對以分析電子穿隧事件之種類。 Chapter 4: 結論、未來展望。;Owing to Coulomb blockade effect, the number of charges in a single-electron system is fixed. The charge in the system can be add or subtract only when energy given to the system is higher than charging energy of the system. With this feature, single-electron devices are suitable for studying single-electron tunneling events, such as Cooper pair splitting or Andreev reflection. We fabricated a normal metal-insulator-superconductor-insulator-normal metal (NISIN) box as a three-island single-electron device. The NISIN-box consists of an aluminum superconductor island (S) and two cupper normal metal islands (N1, N2). S island is linked to N1 and N2 via two insulating barriers (I). Each island couples to a nearby gate electrode capacitively. We apply voltages on the gate electrodes to change the free energy of the NISIN-box, and therefore to force the electrons tunneling within the box. We place two single-electron transistors (SETs) as charge sensors to detect the charge state of the box and tunneling events in the box. SET measurements help us to observe tunneling events. To properly identify all tunneling events, we simulate the stability diagrams of the system to compare the stability diagrams from experiments. The simulated stability diagrams are well matched to the experimental ones, and therefore gives us information for the tunneling events in the NISIN-box. We further study the rate of cotunneling in the NISIN-box, an important error source of the quantum current standard. We could also fabricate a similar NISIN-box to study Cooper pair splitting. Summary of each chapters: Chapter 1: Theorem and application of single-electron device. In our experiment, the main devices we used are hybrid single-electron box and hybrid single-electron transistor. Chapter 2: The information about processes and technologies of the device fabrication. Chapter 3: Simulation of stability diagrams of the NISIN-box. The simulation is compared with the stability diagrams of experiments. Then we can identify the charge tunneling events Chapter 4: Conclusion and future work.
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