We propose two new approaches for regulating spin polarization and spin inversion in a conducting junction within a tight-binding framework based on wave-guide theory. The system comprises a magnetic quantum ring with finite modulation in site potential is coupled to two non-magnetic electrodes. Due to close proximity an additional tunneling is established between the electrodes which regulates electronic transmission significantly. At the same time the phase associated with site potential, which can be tuned externally yields controlled transmission probabilities. Our results are valid for a wide range of parameter values which demonstrates the robustness of our proposition. We strongly believe that the proposed model can be realized in the laboratory.

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Externally controlled high degree of spin polarization and spin inversion in a conducting junction: Two new approaches.

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Several proposals are available to get selective spin transmission through different nano-junctions and in all the cases the regulation is done either by applying a magnetic field or by tuning spin–orbit (SO) coupling. In the present work, we explore a separate scheme where the spin-dependent transport is regulated externally by irradiating a quantum ring that bridges the contact electrodes. This is a new proposal of generating spin selective transmission through a nano-junction, to the best of our knowledge. A high degree of spin polarization along with its phase alteration can be achieved by suitably adjusting the irradiation, circumventing the regulation of magnetic field and/or SO coupling. The effect of irradiation is included through the well-known Floquet-Bloch ansatz, where all the spin-dependent transport phenomena are worked out using Green’s function formalism following the Landauer–Buttiker prescription within a tight-binding framework. Precise dependencies of light irradiation, SO coupling, magnetic flux threaded by the ring, interface sensitivity, system temperature, and impurities on spin polarization are critically investigated. Our analysis may give a new platform for spin selective electron transmission and make it applicable to other complex nano-structured materials also. We strongly believe that the present proposal can be examined in a suitable laboratory.

Selective spin transmission through a driven quantum system: A new prescription

A scheme for a spin-polarized current separator is investigated by studying the spin-dependent electron transport of a fork-shaped nanostructure with Rashba spin-orbit coupling (SOC), connected to three leads with the same width. It is found that two spin-polarized currents are of the same magnitude but opposite polarizations can be generated simultaneously in the two output leads when the spin-unpolarized electrons injected from the input lead. The underlying physics is revealed to originate from the different spin-dependent conductance caused by the effects of Rashba SOC and the geometrical structure of the system. Further study shows that the spin-polarized current with a strong robustness against disorder, demonstrates the feasibility of the proposed nanostructure for a real application.

Spin-polarized current separator based on a fork-shaped Rashba nanostructure

A spin-polarized current direction controller scheme is proposed based on a nonuniform Rashba quantum wire. It is shown that |PLRz| = |PRLz|, whereas their signs are opposite, and the effect of this phenomenon is due to the two broken symmetries and the unbroken C2-rotation symmetry of the investigated system. In addition, the spin-polarized current is nonzero even with a strong disorder strength, which demonstrates that this structure may be utilized for potential applications.

Xiaomao Li

Papers

Spin filtering in a nonuniform quantum wire with Rashba spin–orbit interaction