- 學位論文
奈米錫顆粒之超導與自旋極化間共存及互競現象
Coexistence and Competition between Superconductivity and Spin Polarization in Sn Nanoparticles.
摘要
採用熱蒸鍍法製備錫奈米顆粒，以Sn_071205表示。透 過AFM與X光繞射鑑定‧徑為7 nm，從X光螢光分析與 X光繞射圖分析，確定Sn_071205樣品成份皆為錫，無 氧化物或者其他元素。 由磁化曲線及變溫磁化率曲線可觀察到Sn_071205樣 品同時具有超導抗磁性及自旋極化效應，兩種效應可 以共存。進一步以壓合的方式改變樣品顆‧間距，在 顆粒間距較大的區域，可觀察到超導抗磁性減弱且自 旋極化增強，判斷兩種效應不單只有共存，彼此之間 還會相互競爭。顆粒間距S=9.5 nm時，庖立順磁磁化 率與飽和磁化強度同時具有極大值。於顆粒間距S=6.9 nm時，樣品產生轉變，庖立順磁磁化率與飽和磁化強 度同時逆勢變小，且於實驗溫度1.8 K以上觀察不到超 導抗磁性，之後繼續壓合超導抗磁性又逐漸增強。 探討超導臨界溫度隨顆粒間距變化趨勢，受到超導能 隙Δ以及平均單電子能階分離能隙δ隨顆粒間距變化 的影響，其關係曲線共可區分為四個區域。此外在低 聚合密度的區間，超導抗磁性的減弱使得穿透深度隨 顆粒間距縮短而逐漸加深，與本實驗室去年的研究大 致上相符合。
並列摘要
Sn nanoparticles were fabricated by thermal evaporation method. Atomic force microscope images and x-ray diffraction patterns were performed to examine particle diameter and composition. A pure 7 nm Sn nanoparticle powder was obtained. No trace of oxidation or other impurity was found. AC magnetic susceptibility and magnetization measurements were performed to study the magnetic properties. Superconductivity and spin polarization were observed to coexist at low temperatures. To study the interplay between spin polarization and superconductivity, the M-H curves at different interparticle separations were measured. Coexistence and competition between superconductivity and spin polarization were found for inter-particle separation that is greater than 6.9 nm. No superconductivity may be found at an inter-particle separation of 6.9 nm. As the inter-particle separation was reduced further, the superconductivity signals recovered. The inter-particle interactions linked to the critical temperature can be divided into four regimes. It is the competition between superconductivity and spin polarization that govern the behavior.