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HL: Halbleiterphysik

HL 40: Quantum dots and wires: Optical properties III

HL 40.6: Vortrag

Donnerstag, 30. März 2006, 12:15–12:30, POT 151

Exciton Dephasing in Quantum Dots: An Exactly Solvable Model — •Egor Muljarov and Roland Zimmermann — Institut für Physik der Humboldt-Universität zu Berlin, Newtonstr. 15, D-12489 Berlin

In quantum dots, the nondiagonal phonon coupling is responsible for the two main mechanisms of the dephasing - real and virtual phonon-assisted transitions between different excitonic states which have been recently treated in an approximate way [1]. It turns out, however, that virtual transitions alone can be taken into account by mapping the nondiagonal coupling into a level-diagonal quadratic interaction which can be solved exactly. Surprisingly, the quadratic coupling in quantum dots leads to qualitatively different results in case of acoustic and optical phonons. As shown in [2], virtual transitions with acoustic phonon assistance result in an exponential decay of the optical polarization and a broadening of the zero-phonon line. In contrast, the quadratic coupling to dispersionless optical phonons gives no dephasing at all, which rectifies an approximate treatment by Uskov et al. [3]. In fact, the exact solution shows that the polarization is almost perfectly periodic in time domain, and the absorption spectrum consists of an infinite set of discrete unbroadened lines.

[1] E. Muljarov, T. Takagahara, and R. Zimmermann, Phys. Rev. Lett. 95, 155405 (2005).

[2] E. Muljarov and R. Zimmermann, Phys. Rev. Lett. 93, 237401 (2004).

[3] A.V. Uskov et al., Phys. Rev. Lett. 85, 1516 (2000).