Spin-filter Applications Research Articles

Symmetry-induced perfect transmission and inverse magnetoresistance in cascade junctions of ferromagnet and semiconductor

Within the Landauer framework of ballistic transport, we theoretically investigate spin-dependent resonant transmission and magnetoresistance in symmetric cascade junctions of ferromagnetic metal (FM) and semiconductor (SC). It is shown that spin-up and spin-down electrons possess different bandgap structures against the Rashba spin-orbit wave vector. Due to the mirror symmetry, multiple spin-dependent perfect transmissions of electrons can be obtained within the bandgap, thereafter, spin polarization has multiple reversals. Around each resonant wave vector, high spin polarization is achieved and the electrical conductance comes from one kind of spin electrons. The resonant transmissions originate from the spin-dependent quasi-bound states at energies above the potential barriers, which are demonstrated by the electronic charge distributions in the system. Furthermore, if we change the magnetization of FM in the centre of the junctions, inverse magnetoresistance can be observed. The investigations may have potential applications in spin filters and spin switches.

Spin-dependent bandgap structure and resonant transmission of electrons in ferromagnetic metal/semiconductor cascade junctions

We investigate spin-dependent transport in ferromagnetic metal (FM)/semiconductor (SC) cascade junctions, which can be denoted as (FM∕SC)n∕FM. Here, n is the repeated number of FM/SC junction. In the Landauer framework of ballistic transport, we have calculated the spin-dependent transmission and the spin polarization in these cascade junctions. It is shown that spin-up and spin-down electrons possess different bandgap structures against the Rashba spin-orbit wave vector. As a result, high spin polarization can be achieved. Besides, resonant transmission for spin-up or spin-down electrons can be observed within the bandgap when we intentionally change the magnetization of FM in the center of the cascade junctions. Around resonant wave vector, spin polarization will be reversed. Our investigations may have potential applications in spin filters and spin switches.

Experimental demonstration of split side-gated resonant interband tunneling devices

We report a prototype side-gated asymmetric resonant interband tunneling device (RITD) fabricated with an AlSb∕InAs∕GaSb∕AlSb heterostructure for Rashba spin filter applications. This device features independent control gates along the sides of an RITD mesa structure that can be used to provide an electric field orthogonal to the resonant tunneling current. The distribution of lateral wave vectors for electrons approaching the RITD active layers obtains a nonzero average through the application of the orthogonal electric field, a requirement for Rashba spin filter operation. Measured current–voltage curves show a modulation of the tunneling current with a side gate bias, demonstrating lateral electric-field projection into the resonant tunneling mesa structure. The prototype device was fabricated to submicron dimensions utilizing a conformal and scalable processing scheme.

Theory of spin filtering through quantum dots

Using a nonequilibrium diagram technique for Hubbard operator Green functions combined with a generalization of the transfer Hamiltonian formalism, we calculate the transport through a magnetic quantum dot system with spin-dependent couplings to the contacts. In specific regimes of the parameter space the spin-dependent tunnel current becomes more than 99.95% spin polarized, suggesting that a device thus constructed can be used in spin-filter applications. First-principles electronic structure calculations show the existence of nanostructured systems, such as, e.g., ${\mathrm{M}\mathrm{g}\mathrm{O}/\mathrm{F}\mathrm{e}/\mathrm{P}\mathrm{d}}_{5}/\mathrm{F}\mathrm{e}/\mathrm{M}\mathrm{g}\mathrm{O}$ (001), with the desired properties in the direction of the current.

Modeling spin-dependent transport in InAs/GaSb/AISb resonant tunneling structures

The Rashba effect resonant tunneling diode is a candidate for achieving spin polarizing under zero magnetic field using only conventional non-magnetic III–V semiconductor heterostructures. We point out the challenges involved based on simple arguments, and offer strategies for overcoming these difficulties. We present modeling results that demonstrate the benefits of the InAs/GaSb/AlSb-based asymmetric resonant interband tunneling diode (a-RITD) for spin filtering applications.