Electro-optical generation of patterned electron and nuclear spins in ferromagnet-semiconductor hybrids.

摘要

Semiconductor electronics has thus far been dominated by the manipulation of electronic charge. For most devices it has not been necessary to consider the spin, the inherent quantum-mechanical angular momentum, of the charge carriers. On the other hand the rapid development and implementation of metallic spin-valves, which are inherently spin-dependent devices, has enabled enormous increases in the storage density of magnetic hard-drives, thus becoming a key technological component of modern computers. The goal of the field of semiconductor spintronics is to control and use the spin degree-of-freedom of quantum-mechanical entities in semiconductors to enable new types of devices, while retaining the exquisite control of the electrical and optical properties afforded by several decades of development in the semiconductor industry.; There are at least five general ingredients for spintronics technology including the ability to create, manipulate, move, store, and detect spin polarization. In this work we present new methods potentially useful in the first three aspects, using structures made from a material system composed of epitaxial ferromagnetic metals grown on GaAs via molecular beam epitaxy. The first series of experiments details how one can generate both nuclear and electron spin polarization in the GaAs either optically, electro-optically, or purely electrically. The ability to generate large nuclear spin polarization (approaching 20%) in modest applied magnetic fields enables the possibility of both storing information (in the state of the nuclear spin-system) and manipulating electron spins due to the hyperfine coupling between electron and nuclear spins, albeit at relatively low temperature. These experiments culminate in a new way to generate electron spin polarization all-electrically with the application of a few volts that should in principle work at temperatures greater than room temperature.; The second series of experiments shows how one can pattern arbitrary lateral nuclear spin polarization profiles either optically or by lithographic patterning. This enables the creation of large gradients in the nuclear spin polarization. Again, through the hyperfine coupling, these polarizations and polarization gradients manifest as large effective magnetic fields and field gradients which act upon electron spins. The ability to control the placement and shape of these effective fields and gradients therefore yields a tool that may be useful in spintronics devices based on nuclear spin.