Excitonic effects on the two-color coherent control of interband
transitions in bulk semiconductors
Physical Review B, 72 (7):
075205 (August 2005)Abstract
Quantum interference between one- and two-photon absorption pathways
allows coherent control of interband transitions in unbiased bulk
semiconductors; carrier population, carrier spin polarization, photocurrent
injection, and spin-current injection can all be controlled. We extend
the theory of these processes to include the electron-hole interaction.
Our focus is on photon energies that excite carriers above the band
edge, but close enough to it so that transition amplitudes based
on low-order expansions in k are applicable; both allowed-allowed
and allowed-forbidden two-photon transition amplitudes are included.
Analytic solutions are obtained using the effective-mass theory of
Wannier excitons; degenerate bands are accounted for, but envelope-hole
coupling is neglected. We find a Coulomb enhancement of each two-color
coherent control process and relate it to the Coulomb enhancements
of one- and two-photon absorption. In addition, we find a frequency-dependent
phase shift in the dependence of photocurrent and spin current on
the optical phases. The phase shift decreases monotonically from
pi/2 at the band edge to zero over an energy range governed by the
exciton binding energy. The phase shift is the difference between
the partial-wave phase shifts of the electron-hole envelope function
reached by one- and two-photon pathways.
Description
Second Harmonic generation in semiconductors; excitonic effects