We report on the preparation and superconductivity of metastable γ-Ga islands on Si(111) substrate. The Ga grows in a typical Volmer-Weber mode at a low temperature of 110 K, resulting in formation of Ga nanoislands at various sizes with the identical γ-phase. In-situ low temperature scanning tunneling spectra reveal quantized electronic states in ultrathin Ga islands. It is found that both the lateral size and thickness of the Ga islands strongly suppress the superconductivity. Due to substantial surface energy contribution, the transition temperature Tc scales inversely with the island thickness and the minimum thickness for the occurrence of superconductivity is calculated to be two monolayers.
铁基超导体是继铜氧化合物高温超导体之后于2008年被发现的一类新型高温超导材料.在所有铁基超导体中,β-Fe Se因具有最简单的化学组分和结构而被认为是探索超导机制的理想体系.借助于半导体工业中成熟的分子束外延生长技术,研究者实现了对Fe Se超导薄膜生长、形貌和组分在原子水平上的精确控制,并在此基础上深入研究了其超导性质.最近研究者又把Fe Se薄膜的分子束外延生长拓展到Sr Ti O3(001)衬底,发现单层Fe Se/Sr Ti O3体系的超导转变温度有超过77 K的迹象.这些研究成果为解决高温超导体的配对机制以及进一步提高超导转变温度提供了全新的途径和思路,引起高温超导和材料科学等领域的广泛关注.
