Electronic Properties of Spin Controlled Semiconductor Nanostructures

该小组旨在研究和阐明自旋控制半导体材料和纳米结构的电子结构和输运性质。为此，研究了铁磁半导体及其相关异质结构的生长和加工，这些材料和结构的输运/磁/光学性质，以及电子结构的计算和输运性质的理论。研究结果总结如下：1。由半导体制成的铁磁/非磁三层结构表现出自旋依赖散射、层间耦合和隧穿磁阻。发射极为（Ga, Mn） As的谐振隧道二极管在铁磁转变温度以下表现出自发的电流峰分裂。同时证明了铁磁（Ga, Mn） As电自旋注入非磁性GaAs结构。（H.Ohno等）研究了（in, Mn） As和（Ga, Mn） As在低温下的磁性和输运。我们的一个重要发现是，在相对较低的温度下热处理，晶体质量得到了很大的改善。软x射线吸收实验清楚地表明，这种改善是由于多余的As原子蒸发。（S.Katsumoto et al.）对III-V基稀释磁性半导体（Ga, Mn） As进行了第一性原理电子带结构计算。最近相邻的三维过渡金属自旋之间的磁相互作用对V， Cr， Mn是铁磁性的。（N.Suzuki et al.）我们制备了一种具有高度旋转对称性的人工原子/分子。对于人造原子，(i)类原子性质，如壳填充和服从洪德规则（ii）自旋态随磁场的各种跃迁已经被观察到。对于人工分子，我们研究了新的自旋效应，如自旋阻断、同位自旋阻断、自旋依赖隧道效应等。（Tarucha et al.）

This group was formed to study and elucidate the electronic structure and the transport properties of spin-controlled semiconductoring materials and nanostructures. To this end, the growth and processing of ferromagnetic semiconductors and their related heterostructures, transport/magnetic/optical properties of these materials and structures, and the electronic structure calculation as well as the theory of transport properties were investigated. The summary of the research results is :1. Ferromagnetic/non-magnetic trilayer structures made of semiconductor showed spin-dependent scattering, interlayer coupling and tunneling magnetoresistance. Resonant tunneling diodes with (Ga, Mn) As emitter exhibited spontaneous current peak splitting below the ferromagnetic transition temperature. Also electrical spin-injection from ferromagnetic (Ga, Mn) As into a nonmagnetic GaAs structure was demonstrated. (H.Ohno et al.)2. Magnetism and transport in (In, Mn) As and (Ga, Mn) As at low temperature was studied. One of our important finding is that crystalline quality is much improved by heat treatment at comparatively low temperature. Soft X-ray absorption experiment is making it clear that the improvement is due to the evaporation of excess As atoms. (S.Katsumoto et al.)3. First-principle electronic band-structure calculations are carried on III-V based diluted magnetic semiconductors (Ga, Mn) As. The magnetic interactions between the nearest neighboring 3d transition-metal spins are ferromagnetic for V, Cr, Mn. (N.Suzuki et al.)We have prepared an artificial atom/molecular having a high-degree of rotational symmetry. For artificial atom, (i) atom-like properties such as shell filling and obeisance of Hund's rule and (ii) various transitions of spin states as a function of magnetic field have been observed. For artificial molecules we have investigated novel spin effects such as spin blockade, isospin blockade, spin-dependent tunneling, and so on. (Tarucha et al.)