Abstract
Abstract Electron spin resonance (ESR) was measured on high-mobility two-dimensional electron gases (2DEG) in modulation-doped SiGe/Si quantum wells. We observe a resonance line as narrow as 40 mG, which allows the detection of as few as 10 9 spins in a standard microwave absorption configuration. Longitudinal spin relaxation times T 1 of up to 30 μs were found, which is six to seven orders of magnitude longer than the momentum relaxation times in these samples. Using either gated samples or samples where the 2D carrier density n s can be adjusted persistently by illumination, the ESR signal was recorded as a function of the carrier density. By measuring the integrated ESR absorption the density of states (DOS) at the Fermi level can be derived as a function of n s . The 2D DOS shows a tail, which allows a quantitative extraction of the potential fluctuations.
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