DESTRUCTION OF MAGNETOPHONON RESONANCE IN HIGH MAGNETIC FIELDS FROM IMPURITY AND PHONON SCATTERING IN HETEROJUNCTIONS

Abstract

We present a detailed theoretical calculation to explain the collapse of the magnetophonon resonance (MPR) effect in high magnetic fields in certain high mobility AlGaAs/GaAs heterojunction samples. The magnetoresistivity (ρxx) and the density of states (DOS) are calculated self-consistently. We include the interaction of electrons with background and remote impurities, with acoustic-phonons via deformation potential and piezoelectric coupling, and with optic (LO) phonons. We find that: (i) the DOS is modified strongly by both elastic and inelastic scattering; (ii) the Landau-level (LL) width oscillates with magnetic fields commensurate with the MPR oscillations in ρxx; and (iii) strong impurity scattering leads to a shift of the DOS peaks to lower energy. An increase in LL width will reduce the additional resonant LO-phonon scattering, but also decrease the contribution to ρxx from all scattering mechanisms due to the reduction in DOS. Near the MPR condition there are thus two competing processes: ρxx increases due to LO-phonon scattering; but this increases the LL width and so reduces the contribution to ρxx from elastic scattering. In certain samples we found that the two effects balanced at high magnetic fields resulting in the disappearance of MPR oscillations from ρxx.