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Dipole matrix elements and the nature of charge oscillation under coherent interband excitation in quantum wells.

By R.A. Coles, R.A. Abram, S. Brand and M.G. Burt


An empirical pseudopotential method is used to model two type-I quantum-well systems, allowing the investigation of interband dipole-matrix elements and charge oscillation under coherent optical excitation. Each relevant (microscopically varying) wave function is expressed as an exact envelope-function expansion to which various approximations are made, in analogy with envelope-function methods such as the k⋅p model. The approximation to the quantum-well energy eigenfunctions of a single envelope function multiplying a band-edge zone-center state, the “atomic picture,” is shown to underestimate by orders of magnitude the interband dipole-matrix element. Including terms due to the second band edge, which play only a minor role in the exact envelope-function expansion, provides a good approximation to the true dipole-matrix element, which is significantly greater than the atomic picture predicts. In addition, the effect on the interband charge oscillation of omitting the second band-edge terms is shown to be a reduction of the oscillation from the width of the well to the atomic scale. These results confirm that the earlier results of Burt hold for realistic three-dimensional systems

Publisher: American Physical Society
Year: 1999
DOI identifier: 10.1103/PhysRevB.60.13306
OAI identifier: oai:dro.dur.ac.uk.OAI2:7629

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