Tech Briefs

Theoretical advances could contribute to development of practical devices.

Progress has been made in calculation of spintronic effects in semiconductor nanostructures. The calculations contribute to the body of theoretical knowledge complementing recent experimental advances in generating, transporting, and detecting coherent spin-polarized populations of electron and nuclear spins in semiconductors. The experimental advances have demonstrated that spintronic effects could be harnessed as the basis of novel nanoscale devices. Theoretical advances are needed to understand and extend the experimental advances by enabling inference of previously unknown phenomena from results of experiments and incorporation of these phenomena into realistic models of operation and performance of spintronic devices, including devices that could be used in quantum computation.

The theoretical effort can be characterized as addressing problems arising in the following four fields of interest within the broader discipline of spintronics:

  • Accurate calculations of spin coherence times for electronic systems in nanoscale structures;
  • Theory of inhomogeneous spin transport and spin injection in nonmagnetic and magnetic semiconductors;
  • Theory of coupling between nuclear and electronic spins and the implications for all-optical manipulation of nuclear spins; and
  • Theory of Si/Ge quantum dots in inhomogeneous electric fields.

Most notable among the results of the effort are the following:

  • Progress has been made in calculations of spin-coherence and spin-transport properties in nanoscale semiconductor devices, including calculations of gyromagnetic ratios ("g factors") in quantum dots, and exchange interactions in Si/Ge quantum dots.
  • New devices to effect tuning of electronspin coherence times, devices that would utilize spontaneous generation of spin polarization, and new designs for spin-based teleportation and spin transistors have been proposed. Especially notable is a proposed electron-spinbased device (see figure) in which teleportation would be mediated by single photons, without need for detection of correlated photons (Bell detection).
  • A previously unknown mechanism of spontaneous generation of spin-polarized wave packets at room temperature in nonmagnetic semiconductors has been predicted. This mechanism is denoted the spin Gunn effect because it is a spintronic analog of the Gunn effect (in which microwave oscillations are produced in a semiconductor layer to which is applied an electric field having a strength exceeding a critical value).
  • It has been predicted that orbital-angular- momentum quenching in quantum dots will drive g factors closer to 2 than previously expected.

This work was done by Michael E. Flatté of the University of Iowa for the Army Research Laboratory. For more information, download the Technical Support Package (free white paper) at www.defensetechbriefs.com/tsp under the Physical Sciences category. ARL-0015

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Spintronic Effects in Semiconductor Nanostructures (reference ARL-0015) is currently available for download from the TSP library.

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