在本論文中我們操作了一個可調式的石墨烯-超導垂直穿隧結，主要是在探討無質量狄拉克費米子(Massless Dirac fermion)與庫珀對(Cooper pair)之間的穿隧行為，我們的樣品主要由兩個鈮-石墨烯結串聯而成，並在其上塗佈離子凝膠作為閘極電極，此閘極電極用來控制室溫下的石墨烯費米能階(Fermi level)的位置，當溫度低於鈮臨界溫度(~9K)且石墨烯費米能階被調整到遠離石墨烯中性點(或稱狄拉克點)時，我們觀察到在零源極-汲極電壓(VSD)附近的微分電導有一個明顯的下沉結構，且其下沉結構的特徵接近超導能隙，其明確的表明了超導鈮與石墨烯結的物理穿隧行為，上述特徵會隨著費米能階的改變而產生變化，令人感興趣的是當費米能階被調整到靠近中性點時，其微分電導受到石墨烯起伏的影響變得明顯，我們數據分析指出所當費米能階遠離中性點時，所觀察到的穿隧行為與巴格翏夫方程(Bogoliubov-de Gennes equation)的理論預測一致，而在靠近中性點時，其穿隧行為主要是受到石墨烯不均勻(disorder)的影響與鏡像安德列夫反射(Specular Andreev reflection)。

We implement a tunable vertical graphene-superconductor tunnel junction and aim to investigate the tunneling behaviors between Dirac fermions and Cooper pairs. Our device consists with two serial coupled Niobium (Nb)-Graphene junctions, which are coated with an ionic gel as a top-gate electrode for controlling the Fermi-level (EF) of grapheme at room temperature. When EF is tuned away from the charge-neutral point (CNP or called the Dirac point) of grapheme and the temperature is lower to the critical temperature of Nb (~ 9 K), we observe a clear dip structure of differential conductance in the vicinity of zero-bias source-drain voltage (VSD), and peak features as VSD approaches the superconducting gap, which indicate clear behaviors of a superconducting Nb-graphene junction. The general features aforementioned evolve with EF ; intriguingly the differential conductance becomes fluctuating as EF is tuned closed CNP. Our data analysis suggests the observed tunneling behaviors are consistent with the theoretical predictions based on the approaches of Bogoliubov-de-Genn equation when EF is away from CNP. Near CNP, the tunneling behaviors are dominated by the combinations of the effects of interfacial disorders and specular Andreev reflection.

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