不連續鉛顆粒/單層二硫化鉬系統之超導鄰近效應觀測;Proximity-induced superconductivity in noncontinuous Pb grains/single layer MoS2 device

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题名:	不連續鉛顆粒/單層二硫化鉬系統之超導鄰近效應觀測;Proximity-induced superconductivity in noncontinuous Pb grains/single layer MoS2 device
作者:	陳柏瀚;Chen, Bo-Han
贡献者:	物理學系
关键词:	二硫化鉬;超導鄰近效應;MoS2;Superconducting Proximity effect
日期:	2017-10-05
上传时间:	2018-01-16 10:43:44 (UTC+8)
出版者:	國立中央大學
摘要:	本研究製作不連續鉛顆粒/單層二硫化鉬元件，觀察不連續超導體/半導體界面的超導鄰近效應(Proximity-induced superconductivity)。超導體中超導能隙內的主要電荷載子為古柏電子對(Cooper pair)，在不連續超導體/非超導體界面上，若古柏電子對從超導體進入非超導體，且傳輸於非超導體上沒有因散射(Scattering)而失去同調性(Coherence)，當整個系統達到相位同調(Phase coherence)時可觀察到整個系統轉變為超導態。鍍鉛於單層二硫化鉬、二氧化矽表面且鍍膜厚度較薄時，由於鉛的抗濕潤性(Dewetting)使得鉛會聚集成不連續顆粒(Grains)，當鍍膜厚度越厚，鉛顆粒間距越小，且相較於二氧化矽表面，鉛顆粒在二硫化鉬表面濕潤性(Wetting)較佳，因此在鍍膜厚度為50nm的情況下，鉛於二硫化鉬表面形成薄膜，而在二氧化矽表面則仍是不連續顆粒。本研究先製作鉛膜/單層二硫化鉬元件，並量測鉛膜的臨界溫度(Critical temperature,Tc)、臨界電流(Critical current,Ic)、臨界磁場(Critical field,Hc)等超導態特性。對不連續鉛顆粒/單層二硫化鉬元件藉由鍍上不同厚度且不連續之鉛顆粒，以及調控閘極電壓改變二硫化鉬的載子濃度，期望能在此類型元件上觀察到超導鄰近效應。本研究中表面覆有高分子電解質閘極(Polymer electrolyte gate)之不連續鉛顆粒/二硫化鉬元件於降溫過程電阻值持續下降，但此類元件大部分在量測系統降至最低溫度前元件燒毀，內文分析元件燒毀可能原因並給予改善建議。總結實驗結果觀察到50nm鉛膜/二硫化鉬元件之超導態特性，而不連續鉛顆粒/二硫化鉬元件大部分於降溫過程中燒毀，因此在本研究不連續鉛顆粒/二硫化鉬元件上尚未觀察到超導鄰近效應。 ;We fabricated Lead (Pb) clusters/single-layer molybdenum disulphide (MoS2) devices, and mainly studied proximity-induced superconductivity in the system. Electrons in a superconductor are paired into Cooper pairs in superconducting state. In a non-superconducting material decorated with noncontinous superconductors system, Cooper pairs may diffuse into non-superconducting material. If Cooper pairs transport in non-superconducting material without losing their coherence, we can observe entire system turning into superconducting state. Pb’s dewetting produces self-assembled noncontinous grains on the single-layer MoS2 surface. The spacing between Pb grains decreases with evaporating thicker Pb on the single- layer MoS2 surface. The carrier concentration of single layer MoS2 is tuable by applying gate voltage on devices. By adjusting carrier concentration of MoS2, thickness and spacing of Pb grains, we expect to observe proximity-induced superconductivity in Pb clusters/single layer MoS2 devices. In our experiment, we measured critical temperature、critical current and critical field of Pb film/ single layer MoS2 devices first. By applying voltage on ploymer electrolyte gate, we tuned the carrier concentration of single layer MoS2 and effectively reduced resistance of the devices. However, most of Pb clusters/ single layer MoS2 devices with ploymer electrolyte gate were burned out during cooling down process. Therefore, we have not observed proximity-induced superconductivity in Pb clusters/single layer MoS2 devices yet. We only observed superconductivity in 50nm Pb film/ single layer MoS2 devices.
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