Current electronic devices store information in the form of electronic charges, but spin, a unique quantum property of electrons, offers an alternative. The spin can be controlled using polarized light to store information. Spin-polarized electrons, or spins aligned in a particular direction, are produced when a polarized light beam interacts with electron spins in a semiconductor.
So far, only uniformly polarized light, that is, light with a spatially uniform polarization, has been used to control electron spins. However, the production of spatially structured electron spins depends on the presence of an additional spatial structure (variation) in the polarization. This offers new possibilities for information storage.
To this end, a group of researchers, led by Junior Associate Professor Jun Ishihara of and including Graduate Student Takachika Mori, Graduate Student (at the time of the study) Takuya Suzuki, and Professor Kensuke Miyajima of Tokyo University of Science (TUS), Japan has now devised a method to generate such spatially structured electron spins using a structured light with a spatially varying polarization profile.
Scientists have successfully generated a structured light beam with spatially anomalous polarization and transferred its structure to electron spins confined in a solid semiconductor. In addition, they simultaneously generated two phase-reversed spin waves using this beam. Their results have essential implications for optical communication and information storage.
Junior associate professor Jun Ishihara said: “In this work, we generated a doughnut-shaped structured light – a vector optical vortex beam with an orbital angular momentum (OAM) – from a basic Gaussian beam using vortex half-wave plate and quarter-wave plate devices. We then used this beam to excite the electron spins that are trapped in a quantum well of a gallium arsenide/aluminium gallium arsenide semiconductor, and these spins in turn formed a spiral spatial structure in a circle.”
Interestingly, while the radius with an OAM number equal to one produced a helix with two spin periods – spin up and spin down around the circle, an OAM number of two resulted in a helix with four such changes. These observations indicated that the spatial polarization structure of the optical vortex determined by the OAM was transferred to the electron spins in the semiconductor.
In addition, it was proposed to increase the OAM number to allow a higher information storage capacity, characterized by a higher repetition rate around the circle.
Interestingly, while the radius with an OAM number equal to one produced a helix with two spin periods – spin up and spin down around the circle, an OAM number of two resulted in a helix with four such changes. These observations indicated that the spatial polarization structure of the optical vortex determined by the OAM was transferred to the electron spins in the semiconductor. In addition, it was proposed to increase the OAM number to allow a higher information storage capacity, characterized by a higher repetition rate around the circle.
Dr Ishihara said: “The conversion of the spatial polarization structure of light into a spatial structure of spin, together with the generation of new spin-spatial structures in combination with effective magnetic fields in solids, is expected to lead to elementary technologies for higher-order quantum media conversion and information capacity. improvement using spin textures.”
Magazine reference:
- Jun Ishihara, Takachika Mori et al. Imprinting spatial helicity structure of vector vortex beam on spin texture in semiconductors. Physical assessment letters. DOI: 10.1103/PhysRevLett.130.126701
