Absence of Magnetophonon Resonance at High Magnetic Fields in GaAs-GaAlAs Heterojunctions

D.R. Leadley¹, R.J. Nicholas¹, W. Xu², F.M. Peeters², J.T. Devreese², J.J. Harris³, C.T. Foxon⁴, J. Singleton^1,5, J.A.A.J. Perenboom⁵, L. van Bockstal⁶ and F. Herlach⁶

1. Deptment of Physics, University of Oxford, Clarendon Laboratory, Parks Road, Oxford, OX1 3PU, UK
2. Departement Natuurkunde, Universiteit Antwerpen (UIA), Universiteitsplein 1, B-2610 Antwerpen, Belgium
3. Department of Electronics and Electrical Engineering, University College London, WC1E 6BT, UK
4. Department of Physics, University Park, Nottingham, NG7 2RD, UK
5. Univerisity of Nijmegen, Toerooiveld 1, NL-6525 ED, Nijmegen, The Netherlands
6. Katholieke Universiteit Leuven, Celestijnenlaan 200 D, B-3001, Leuven, Belgium.

In high mobility GaAs-GaAlAs heterojunctions with low electron density we find magnetophonon resonances (MPR) vanish at high magnetic fields. This is extremely surprising since in all other systems MPR becomes stronger at higher fields. We explain this disappearance by considering all the scattering processes that affect r_xx. At the resonance condition optic phonon scattering (OPS) is maximised. This gives maxima in r_xx when OPS is dominating transport. At low densities we have shown however that elastic scattering dominates r_xxat high B up to ~150 K. Under these conditions the additional broadening due to OPS leads to a compensating fall in the elastic scattering rate and the oscillations disappear. We have performed self consistent calculations which show oscillations in Landau level width and reproduce the experimental r_xx --- including the vanishing of the MPR!

Presented at: Institute of Physics, Condensed Matter and Materials Physics Conference, Sheffield, 1992