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Spintronic Effects in Semiconductor Nanostructures

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

Topics:
Electronic control systems Electronic equipment Magnetic materials Physical Sciences Research and development Semiconductor devices Semiconductors Transistors
This Brief includes a Technical Support Package (TSP).
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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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    Defense Tech Briefs Magazine

    This article first appeared in the April, 2007 issue of Defense Tech Briefs Magazine (Vol. 1 No. 2).

    Read more articles from the archives here.

    Overview

    The document titled "Spin Coherence in Semiconductor Nanostructures," authored by Michael E. Flatté, presents significant advancements in the understanding of spin coherence and transport properties in nanoscale semiconductor structures. The report outlines the progress made in theoretical calculations and experimental observations related to spin-polarized populations of electron and nuclear spins, which are crucial for the development of novel spintronic devices.

    The introduction highlights the recent experimental breakthroughs in generating, transporting, and detecting coherent spin-polarized populations, demonstrating spin coherence times exceeding 100 nanoseconds and spin diffusion lengths over 100 micrometers. These findings suggest the feasibility of utilizing spin phenomena in nanoscale electronics, paving the way for innovative device architectures.

    The report identifies four primary research directions supported by the grant:

    1. Accurate Calculations of Spin Coherence Times: The document discusses the dominant mechanism of spin decoherence, particularly precessional decoherence, which is influenced by inversion asymmetry in materials. The research predicts significant tuning of spin lifetimes in (110) semiconductor quantum wells, which can inform the design of new spin transistors.

    2. Theory of Inhomogeneous Spin Transport: This section addresses the complexities of spin transport in both nonmagnetic and magnetic semiconductors, emphasizing the need for a theoretical framework to understand experimental results and suggest new phenomena.

    3. Nuclear Spin Coupling to Electronic Spin: The implications of this coupling for all-optical manipulation of nuclear spins are explored, indicating potential advancements in quantum information processing.

    4. Theory of Si/Ge Quantum Dots: The report examines the behavior of quantum dots in inhomogeneous electric fields, contributing to the understanding of spin dynamics in these systems.

    The document also discusses the potential applications of these findings in semiconductor spintronic devices and quantum computation, including a novel proposal for electron-spin-based teleportation mediated by single photons. The research indicates that electric transport in nonmagnetic semiconductors may lead to the formation of spin-polarized packets at room temperature, which could have significant implications for future technologies.

    Overall, the report emphasizes the importance of theoretical work in guiding experimental efforts and enhancing the understanding of spin-related phenomena in semiconductor nanostructures, ultimately contributing to the advancement of spintronics and quantum computing.

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