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Science 9 June 1995:
Vol. 268. no. 5216, pp. 1460 - 1463
DOI: 10.1126/science.7539550
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Articles

Science, Vol 268, Issue 5216, 1460-1463
Copyright © 1995 by American Association for the Advancement of Science

articles

Electronic states in gallium arsenide quantum wells probed by optically pumped NMR

R Tycko, SE Barrett, G Dabbagh, LN Pfeiffer, and KW West

AT&T Bell Laboratories, Murray Hill, NJ 07974, USA.

An optical pumping technique was used to enhance and localize nuclear magnetic resonance (NMR) signals from an n-doped GaAs/Al0.1Ga0.9As multiple quantum well structure, permitting direct radio-frequency measurements of gallium-71 NMR spectra and nuclear spin-lattice relaxation rates (1/T1) as functions of temperature (1.6 K < T < 4.2 K) and the Landau level filling factor (0.66 < v < 1.76). The measurements reveal effects of electron-electron interactions on the energy levels and spin states of the two-dimensional electron system confined in the GaAs wells. Minima in 1/T1 at v approximately 1 and v approximately 2/3 indicate energy gaps for electronic excitations in both integer and fractional quantum Hall states. Rapid, temperature-independent relaxation at intermediate v values indicates a manifold of low-lying electronic states with mixed spin polarizations.


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