All-Electric Semiconductor Spin Valve

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A concerted experimental and theoretical research program is proposed to develop an all-electric, lateral spin valve with a large (~ 30) On/Off conductance ratio. The device will be made from gallium arsenide and will not use any ferromagnetic electrodes or external magnetic field to flip the electron spin. It consists of two quantum point contacts in series separated by a short one-dimensional conduction channel of length smaller than the spin coherence length of gallium arsenide at the temperature of operation. Each quantum point contact acts as all-electric spin polarizer or detector and can provide or filter almost completely spin-polarized current. Non-equilibrium Green¡¦s function simulation of model devices indicate that spin valve devices based on gallium arsenide quantum point contacts on length scale of tens of nanometers, achievable with modern lithographic technology, can yield a large enough spin splitting to make feasible operation at ambient temperature with large On/Off conductance ratio.Intellectual meritThe creation, manipulation, and detection of spin-polarized currents by purely electrical means are challenging goals in semiconductor spintronics. Spin valves so far studied have used ferromagnetic electrodes or material embedded into device architecture for spin polarization and detection and an external magnetic field to flip the spin. Very recently, we have demonstrated that quantum point contact made from the semiconductor indium arsenide can be used to generate strongly spin polarized current by purely electrical means when its confining potential is made highly asymmetric by gate bias voltages. The spin valves based on gallium arsenide quantum point contacts we will develop in this project are unique in two respects. First, all-electric quantum point contacts will be used as spin polarizer and detector. Second, a one-dimensional transport channel is used that offers a number of advantages over two-dimensional channels used so far. Finally, because of the long (tens of micrometers) spin coherence length of gallium arsenide relative to that (tens of nanometers) of indium arsenide at room temperature, operation of the gallium arsenide spin valves at ambient temperature is feasible. If successful, this project will be ground-breaking. Broader ImpactsThe success of this project is expected to stimulate the development of all-electric, ultra high-speed, energy-efficient spin valve devices that can be used for high-speed digital information processing and eventually in solid-state quantum computation based on spin qubits. This project, if successful, will be a major milestone and a breakthrough in semiconductor spintronics. A goal of this project is to develop the first simulator based on non-equilibrium Green¡¦s function technique to model spin transport in nanoscale devices and make it available to the scientific community at large via the nanoHUB website. Both graduate and undergraduate students will participate in this research effort. This project will specifically engage undergraduate physics/engineering students of Xavier University and the University of Cincinnati to cutting edge physics research and advanced techniques not accessible in traditional undergraduate programs and courses.