Enhancement of Shubnikov-de Haas oscillations by carrier modulation

A drastic enhancement of the Shubnikov-de Haas (SdH) pattern is obtained by recording the changes in the quantum oscillations of magnetoresistance due to modulation of the carrier concentration. The technique enables measurement of the SdH waveform at relatively high temperatures and in samples with moderate mobilities. The modulated waveform shows selective enhancement of the low-frequency SdH oscillations associated with the upper subband. Thus, we were able to record very clear oscillations generated by a carrier concentration well below 5×10¹⁰ cm^-2. The theory for this selective enhancement is provided.