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    Please use this identifier to cite or link to this item: http://ir.lib.ncu.edu.tw/handle/987654321/66820

    Title: 石墨烯與超導金屬介面的電子穿隧行為
    Authors: 柯億謙;Ke,Yi-chien
    Contributors: 物理學系
    Keywords: 石墨烯;半導體/超導體混合式元件;古柏對分裂;彈性共同穿隧
    Date: 2014-12-03
    Issue Date: 2015-03-16 15:41:03 (UTC+8)
    Publisher: 國立中央大學
    Abstract: 電子在超導體中以古柏對形式存在,古柏對是量子糾纏電子對,可以透過交叉式安德烈夫反射將古柏對裡的兩個電子分別穿隧至兩個空間上分離的一般金屬,這種空間上分離的糾纏電子對可以應用在固態量子傳輸上。為了提高古柏對分裂的效率,可以利用兩個有不同電荷傳輸載子類型的半導體來取代一般金屬,因為p型半導體(n型半導體)只允許電洞(電子)存在於超導體/半導體介面。
    我們製作石墨烯/鋁/石墨烯元件,鋁金屬在溫度1.1K以下為超導體,石墨烯與鋁金屬介面透過穿隧屏障相接,兩塊石墨烯有一個全域的下閘極以及兩個獨立的上閘極來調控其載子種類與濃度。本論文研究元件的二階(2nd order)電子穿隧行為,包括古柏對分裂與彈性共同穿隧。
    ;Cooper pair in superconductor is a quantum entangled object and could split into two spatially-separate normal metals via crossed Andreev reflection. Such spatially-separate entangled electron pair may have applications to solid-state quantum teleportation. To achieve high efficiency of Cooper pair splitting (CPS), two semiconductors with opposite polarities are proposed to replace two normal metals due to either electron or hole is missing in both superconductor/semiconductor interfaces.
    We fabricated graphene/aluminum/graphene devices. Aluminum becomes superconducting below 1.1K and it links to two graphene grains via tunneling barriers. Each graphene can be tuned electrically by a global bottom-gate and a local top-gate. This thesis reported studies of electrons 2nd-order tunneling events in the devices, including CPS and elastic cotunneling (EC).
    According to the non-local voltage and current-current correlation measurements, we mostly observed EC. EC is enhanced when the aluminum becomes superconducting. In a small region near Vbg=10V, two graphene grains have opposite polarities, making a p-type graphene/superconductor/n-type graphene (pSn) device. We found minimum value of non-local voltage when Vbg=10V. The decrease of nonlocal voltage implies CPS. Because the low quality of top-gates, we are unable to vary carrier density of two graphene grains independently. Therefore, we cannot make pSn device reliably. The study of electrons tunneling events in pSn device requires further investigation.
    Appears in Collections:[物理研究所] 博碩士論文

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