Based on the correspondence between the conventional Poincaré and Bloch spheres, we proposed a higher-order Bloch spheres, which is an extension of the conventional Bloch spheres. By calculating the expectation value of the spin components using the Pauli spin matrices, we found that the new spin state is formed in a ring shape and the orientation of the spin changes depending on the azimuthal angle and topological charge of orbital angular momentum. We also realize the coherent transfer of the azimuth-dependent polarization state of photons to the electron spin state in a GaAs quantum well with a V-shaped three-level system.
Long-range spin transport at room temperature is one of the indispensable technologies for realizing spintronics devices. In this study, we have investigated electron spin relaxation time of (110)-oriented GaAs superlattice having tunnel-coupled quantum wells for both lateral and vertical spin transport. It was revealed that the spin relaxation time at room temperature was 0.7 ns, about 7 times longer than that of bulk GaAs which has been used for conventional spin transport layer of spin-controlled lasers. This finding provides a novel method of controlling the spin relaxation time at room temperature and indicates that the superlattice structures are promising for spin transport layers in semiconductor-based spintronics devices.
(110)-oriented GaAs-based quantum wells (QWs) are promising active layers of spin lasers because of long spin relaxation time at room temperature. So far, (110)GaAs/AlGaAs QWs have been investigated intensively and long carrier lifetime of several ns has been reported. In contrast, there have been few reports on the crystal growth of (110)InGaAs/(Al)GaAs QWs despite its great potential to the active layer, resulting in rather poor crystal quality with short carrier lifetime. In this study, we tried to grow high-quality (110)InGaAs/(Al)GaAs QWs by optimizing MBE growth conditions and obtained long carrier and spin lifetime (>1 ns) in the QWs grown with relatively high temperature and As/Ga flux ratio. This reveals that the (110)InGaAs/(Al)GaAs QWs are applicable to the active layer of spin lasers. In addition, we propose a novel structure for a spin transport layer between the ferromagnetic electrode (spin injector) and the active layer of spin laser.
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