Anomalous resonance phenomena in two-dimensional electrons on the surface of ³He-⁴He liquid mixtures

We report on anomalous resonance phenomena observed in a two-dimensional electron system on ³He-⁴He liquid mixtures. The resonance is observed in a Corbino conductivity measurement, in which a magnetic field B is applied prependicular to the electron sheet. We have detected the resonances for ³He concentrations n₃ from 0.475% to 10.20%, and at temperatures below 800 mK. The resonance frequency f_r is inversely proportional to B. In a preliminary study we found that f_r and the resonance amplitude increases when the electron sheet is not parallel to the electrode, and this made the understanding difficult. Here we have made the systematic measurement keeping the parallelism between the electrons and the electrode. We have observed the resonance only at n₃ > 0.475%. This fact finally leads us to conclude that adding ³ He atoms to liquid ⁴He induces the nonuniformity in local electron density, and hence the resonance.