Level crossing in the two-dimensional electron system in the presence of gigantic Zeeman effect and quantum Hall ferromagnet

本研究项目的主要目的是澄清“磁性”二维电子气体（2DEG）特有的物理性质，这些物理性质是由二维电子与磁性离子的局域矩之间的交换相互作用产生的。我们利用分子束外延技术（MBE）生长了由稀释磁性半导体Cd_<1-x>Mn_xTe的阱层和Cd_<1-y>Mg_yTe的势垒层组成的调制掺杂异质结构，并研究了它们的磁输运和磁光性质。为了获得高迁移率的“磁性”2DEG，我们首先在CdTe/Cd_<1-y>Mg_yTe的非磁性异质结构的MBE生长中尝试了几种发明。结果表明，利用氢等离子体清洗GaAs（001）衬底表面可以有效去除氧化表面层。在Cd_<1-x>Mn_xTe/Cd_<1-y>Mg_yTe的生长中也采用了这种氢清洗方法，我们成功地制备了高迁移率的磁性2DEG。在强磁场下的磁输运和磁光测量中，我们发现了磁性2DEG特有的反常行为，如在整数填充因子的磁场中，激子发光的能量依赖于磁场的突然跳跃。此外，我们还利用光刻和刻蚀制备的磁性2DEG样品顶部的栅极，实现了场效应晶体管结构中二维电子密度的连续控制。在施加栅极电压连续改变二维电子密度的磁输运和磁光测量中，我们发现了磁电阻率、霍尔电阻率和发光能量在磁场依赖性中的异常行为，这是普通整数量子霍尔效应无法解释的。我们分析了这些异常行为是由于量子霍尔铁磁体的影响，它起源于不同自旋取向的朗道能级之间的交叉。少

The main purpose of this research project is clarifying the physical properties peculiar to the "magnetic" two-dimensional electrons gas (2DEG) originating from the exchange interaction between the 2D electrons and the localized moments of magnetic ions. We have grown modulation-doped heterostructures consisting of the well layer of diluted magnetic semiconductor Cd_<1-x>Mn_xTe and the barrier layer of Cd_<1-y>Mg_yTe by molecular beam epitaxy (MBE) and have investigated the magneto-transport and magneto-optical properties. In order to obtain high-mobility "magnetic" 2DEG, we have first tried several inventions in the MBE growth of non-magnetic heterostructures of CdTe/Cd_<1-y>Mg_yTe. As a result, it was confirmed that the cleaning the surface of a GaAs (001) substrate using hydrogen plasma is effective for removing the oxidized surface layer. By adopting this hydrogen cleaning method also in the growth of Cd_<1-x>Mn_xTe/Cd_<1-y>Mg_yTe, we have succeeded in fabricating high-mobility mag … More netic 2DEG. In the magneto-transport and magneto-optical measurements under high magnetic fields, we have found anomalous behaviors peculiar to magnetic 2DEG, such as an abrupt jump in the magnetic field dependence of energy of the excitonic luminescence at a magnetic field of an integer filling factor. In addition, we have achieved a continuous control of the 2D electron density in the field-effect transistor structure with a gate electrode on the top of the magnetic 2DEG sample fabricated by the photolithography and we etching. In the magneto-transport and magneto-optical measurements under the continuous change of the 2D electron density by applying a gate voltage, we have found anomalous behaviors in the magnetic field dependence of magnetoesistivity, Hall resistivity, and the luminescence energy, which cannot be explained by ordinary integer quantum Hall effect. We have analyzed that these anomalous behaviors are due to the effect of quantum Hall ferromagnet, which originates from the crossing between Landau levels with different spin orientations. Less