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Published December 23, 2008 | Published + Supplemental Material
Journal Article Open

Imaging quantum confinement with optical and POWER (perturbations observed with enhanced resolution) NMR


The nanoscale distributions of electron density and electric fields in GaAs semiconductor devices are displayed with NMR experiments. The spectra are sensitive to the changes to the nuclear-spin Hamiltonian that are induced by perturbations delivered in synchrony with a line-narrowing pulse sequence. This POWER (perturbations observed with enhanced resolution) method enhanced resolution up to 103-fold, revealing the distribution of perturbations over nuclear sites. Combining this method with optical NMR, we imaged quantum-confined electron density in an individual AlGaAs/GaAs heterojunction via hyperfine shifts. Fits to the coherent evolution and relaxation of nuclei within a hydrogenic state established one-to-one correspondence of radial position to frequency. Further experiments displayed the distribution of photo-induced electric field within the same states via a quadrupolar Stark effect. These unprecedented high-resolution distributions discriminate between competing models for the luminescence and support an excitonic state, perturbed by the interface, as the dominant source of the magnetically modulated luminescence.

Additional Information

© 2008 by The National Academy of Sciences of the USA. Edited by Alexander Pines, University of California, Berkeley, CA, and approved November 11, 2008 (received for review July 7, 2008). This article is a PNAS Direct Submission. Published online before print December 22, 2008, doi: 10.1073/pnas.0806563106 We thank Frank Grunthaner of the National Aeronautics and Space Administration Jet Propulsion Laboratory for providing the sample, Doran Smith of the U.S. Army Research Laboratory for the Schrödinger–Poisson solver used to calculate the interfacial E field, and Lou Madsen of Virginia Tech for critical reading of the manuscript. This work was supported by National Science Foundation Grant CHE-9612226. Author contributions: J.G.K., M.A.M., and D.P.W. designed research; J.G.K. and M.A.M. performed research; J.G.K. and M.A.M. analyzed data; and J.G.K. and D.P.W. wrote the paper. The authors declare no conflict of interest. This article contains supporting information online at www.pnas.org/cgi/content/full/0806563106/DCSupplemental.

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