Influence of the second subband on the surface acoustic wave transmission in the quantum Hall regime

摘要

The attenuation of surface acoustic waves (SAWs) propagating through an asymmetric two-layer system is investigated in the quantum Hall regime. The position of the Fermi level is varied in the vicinity of the population threshold of the second subband by changing the electron density and by injecting a dc current. For large currents, the quantum Hall effect (QHE) breaks down. The SAW attenuation in the breakdown regime reveals that the vanishing conductivity of the QHE is maintained in the interior of the sample despite its absence from the resistance. The inhomogeneous breakdown of the QHE becomes more apparent when the Fermi level approaches the second subband level. When the electron population in the second subband is significantly large, the SAW transmission develops gigantic structures at the quantum Hall states. A drastic variation of the screening properties associated with the relocation of electrons between the two layers is responsible for the behaviour. The observation of a hysteretic behaviour evidences that the SAW-generated electric fields are strong enough to influence the interlayer charge transfer.