Mesoscopic magnetism and electronic transport

9-1介观超导体的类磁通态单电子晶体管结构是研究介观材料超导态的最佳系统之一，原因如下。（1）由于能隙是通过电输运直接测量的，所以灵敏度非常高。（2）这种结构的两个隧道结使介观超导体隔离良好，与周围环境的耦合最小，利用这种结构，我们证明了尽管岛上库珀对的数目几乎固定，介观超导环的序参量仍保持空间单值性。我们还发现，在简单连接的超导体中（即没有空穴的超导体），序参量的振幅在材料表面很大。9 -2二维电子系统的磁装饰我们通过铁磁体的纳米制造引入了介观尺度的周期性磁调制。由于应变和镜像力不可避免地会引入较大的静电调制效应，使得磁调制效应难以检测。利用铁磁体的磁滞效应解决了这个问题，并给出了清晰的观察结果。9 -3稀磁半导体的低温输运稀磁半导体（Ga，Mn）As的首次成功生长被报道。我们还发现了在铁磁相的巨磁阻。在（In，Mn）As/GaSb异质结中发现了光致铁磁性。

9-1 Fluxoid states of mesoscopic superconductorsIt has been shown that the single-electron transistor structure is one of the best systems to investigate the superconducting states of mesoscopic materials by the following reasons.(1)Because the energy gap is directly measured through the electric transport, the sensitivity is very high.(2)The mesoscopic superconductor is well-isolated by the two tunnel junctions of the structure and the coupling to the surrounding environment is minimized.Using this structure, we have shown that the order parameter of mesoscopic superconducting ring keeps its spatial single-valuedness though the number of the Cooper pair on the island is almost fixed. We found, also, that in the simply-connected superconductor (i.e.that without hole) the amplitude of the order parameter is large at the surface of the material.9-2 Magnetic decoration of two-dimensional electron systemsWe introduced periodic magnetic modulation of mesoscopic scale by nano-fabrication of ferromagnets. It had been difficult to detect the effect of the magnetic modulation because of the large effect of electrostatic modulation inevitably introduced by the strain and the image force. The problem was solved by utilizing the hysteresis effect of the ferromagnets and the clear observation was achieved.9-3 Low temperature transport of diluted magnetic semiconductorsThe first successful growth of a diluted magnetic semiconductor (Ga, Mn) As was reported. We also found colossal magnetoresistance in the ferromagnetic phase. Light-induced ferromagnetism was found in (In, Mn) As/GaSb heterostructure.