Solid State Nuclear Magnetic Resonance 29 (2006) 52–65 Dynamic nuclear polarization and nuclear magnetic resonance in the vicinity of edge states of a 2DES in GaAs quantum wells Clifford R. Bowers a,Ã , Joshua D. Caldwell b , Guennadi Gusev c , Alexey E. Kovalev d , Eugene Olshanetsky e , John L. Reno f , Jerry A. Simmons f , Sergey A. Vitkalov g a Department of Chemistry and the National High Magnetic Field Laboratory, University of Florida, P.O. Box 117200, Gainesville, Florida 32611-7200, USA b Naval Research Lab, Power Electronics, 4555 Overlook Ave, S.W., Code 6881, Washington, DC 20375, USA c Instituto de Fı´sica, Universidade de Sa˜o Paulo, Caixa Postal 66318, 05315-970, Sa˜o Paulo, SP, Brasil d Department of Electrical Engineering, Pennsylvania State University, State College, PA, USA e Institute of Semiconductor Physics, Novisibirsk, Russia f Sandia National Laboratories, MS 1415, Albuquerque, NM 87185, USA g City College of New York at CUNY, Physics Department J-419, Convent Avenue at 138th Street, New York, NY 10031, USA Received 5 July 2005; received in revised form 23 August 2005 Available online 10 October 2005 Abstract Nuclear magnetic resonance is detected via the in-plane conductivity of a two-dimensional electron system at unity Landau level filling factor in the regime of the quantum Hall effect in narrow and wide quantum wells. The NMR is spatially selective to nuclei with a coupling to electrons in the current carrying edge states at the perimeter of the 2DES. Interpretation of the electron-nuclear double resonance signals is facilitated by numerical simulations. A new RF swept method for conductivity-detected NMR is introduced which offers more efficient signal averaging. The method is applied to the study of electric quadrupole interactions, weakly allowed overtone transitions, and evaluation of the extent of electron wave function delocalization in the wide quantum well. r 2005 Elsevier Inc. All rights reserved. Keywords: Quantum well; Parabolic Quantum well; ENDOR; Two-dimensional electron system; Quantum Hall effect; GaAs; DNP; Fictitious spin-1/2; Overtone transitions 1. Introduction Recent interest in spin-based electronics and quantum computing has stimulated numerous experimental and theoretical studies of spin-related phenomena in solid-state semiconductor nanostructures. Magnetic resonance spec- troscopy is the ideal tool for evaluating spin interactions, spin-lattice relaxation times and coherence dephasing mechanisms in potential candidate materials for spin-based device applications. Transport detection of magnetic resonance affords several key advantages over conven- tional resonant cavity or tuned coil methods in quantum confined semiconductors. Most importantly, the limited number of electron or nuclear spins in a nanostructure such as a single quantum dot or quantum well (QW) presents a challenge to the sensitivity of tuned coil or bridge techniques. The inefficiency of detecting MHz or GHz frequency photons is not relevant to optical or charge transport-based detection. Transport detection provides direct access to the spin Hamiltonian and spin relaxation mechanisms relevant to the operation of spin-based devices because the spectroscopy is selective to the conduction channel. Information pertaining to defects [1,2], tunneling [3], and symmetry breaking interactions, which can produce electric quadrupole splittings in NMR [1,4–10] and electron g-factor anisotropy [11–14], can be obtained. Nuclear spin relaxation is found to be extremely sensitive to Landau Level filling [14–16]. The Knight shift [17,18] (i.e. the shift of the nuclear spin Larmor frequency due to coupling to the polarized conduction electron system) can be used to map the electronic wavefunction [19,20] and to ARTICLE IN PRESS www.elsevier.com/locate/ssnmr 0926-2040/$ - see front matter r 2005 Elsevier Inc. All rights reserved. doi:10.1016/j.ssnmr.2005.08.011 Ã Corresponding author. Fax: +1 352 392 8758. E-mail address: cliff.bowers@gmail.com (C.R. Bowers).