Quantum dots due to the flux line lattice in the hybrid structure of diluted magnetic semiconductors and superconductors and its application

在ii型超导体的混合状态下，由于磁通量的规则分布，磁通量密度在表面发生空间调制。在ii型超导体表面附着稀释磁性半导体（DMS）的杂化结构中，期望通过上述场调制调制DMS的有效带隙，并通过超导体中的通量线晶格实现零维量子约束。在本课题中，我们尝试用MBE生长技术制备Cd_<1-x> Mn_xTe和NbSe_2的杂化结构。NbSe_2为层状晶体结构，层间的耦合是由范德华力引起的。在层状晶体上生长的锌-闪锌矿晶体结构CdTe或Cd_<1-x> Mn_xTe属于准范德华外延的范畴；也就是说，层状晶体表面没有悬垂的波，在此基础上生长的锌闪锌矿晶体即使失配33%也不会产生界面应变。在原位观察的RHEED图像中，NbSe_2的条纹图案连续转变为CdTe（111）表面的条纹图案，表明在生长的最初阶段就实现了二维生长。光致发光（PL）测量表明，生长的晶体具有良好的光学质量，激子发射线宽窄。为了研究NbSe_2中磁通量对磁场调制的影响，我们对NbSe_2上生长的Cd_<1-x>Mn_xTe薄膜和Cd_<1-x>Mn_xTe/Cd_<1-y> Mn_yTe单量子阱（SQW）进行了磁致发光测量。在低于4.2K的低温下，激子发射线宽表现出异常行为；即线宽随磁场的增大先增大，然后达到最大值，随着磁场的进一步增大而减小。这种异常行为可以理解为由于通量线晶格引起的场调制效应。少

In the mixed state of type-II superconductors, the spatial modulation of magnetic flux density takes place on the surface due to the regular distribution of magnetic flux. In the hybrid structure in which diluted magnetic semiconductors (DMS) are attached on the surface of type-II superconductors, it is expected that the effective band-gap of DMS is modulated by the above field modulation and quantum confinement in the zero-dimension is realized by the flux line lattice in the superconductors. In the present research project, we have tried to fabricate the hybrid structure of Cd_<1-x> Mn_xTe and NbSe_2 by MBE growth technique.NbSe_2 is of the layered crystal structure, in which the coupling between the layers is due to van der Waals force. The epitaxial growth of the zinc-blende crystal structure, CdTe or Cd_<1-x> Mn_xTe in the present case, on the layered crystal belongs to the category of quasi-van der Waals epitaxy ; that is, the surface of the layered crystal is free of dangling bo … More nds, onto which it is expected the zincblende crystal is grown without interface strain even with a mismatch of 33%. In in situ observation of the RHEED image, the streak pattern of NbSe_2 was transformed into that of CdTe(111) surface continuously, which showed that the two-dimensional growth was achieved at the very initial stage of the growth. Photoluminescence (PL) measurements of the grown crystals showed a good optical quality with a narrow linewidth of the exciton emission.In order to examine the effect of the magnetic field modulation due to the magnetic flux in NbSe_2, we have performed magneto-PL measurements on Cd_<1-x>Mn_xTe films and Cd_<1-x>Mn_xTe/Cd_<1-y> Mn_yTe single quantum well (SQW) grown on NbSe_2. At low temperatures less than 4.2K, the linewidth of the excitonic emission showed anomalous behaviors ; that is, the linewidth first increased with magnetic fields, then took maximum, and decreased with the further increase of magnetic fields. This anomalous behavior could be understood as the effect of the field modulation due to the flux line lattice. Less