The magnetoconductivity $\sigma \mathrm{}\left(B\right)\mathrm{}$ of two-dimensional electrons on liquid helium was measured above 1 K, using high-precision Corbino electrodes. In low magnetic fields $B$, $\frac{\sigma \mathrm{}\left(0\right)\mathrm{}}{\sigma \mathrm{}\left(B\right)\mathrm{}}=1+{\left(\mu B\right)}^2$ as in the Drude model, where $\mu$ is the zero-field mobility due to scattering by ${}_{}{}^4{}_{}{}^{}\mathrm{He}$ vapor atoms, even for $\mu B\gg 1$. At higher fields $\frac{\sigma \mathrm{}\left(0\right)\mathrm{}}{\sigma \mathrm{}\left(B\right)\mathrm{}}$ becomes density dependent due to many-electron effects, in excellent agreement with the theory of Dykman. Only at the highest fields, or the lowest densities, does $\sigma \mathrm{}\left(B\right)\mathrm{}$ approach the theoretical single-particle magnetoconductivity.

• Received 25 April 1994

DOI:https://doi.org/10.1103/PhysRevLett.73.1142