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Author: Thomas G. Pedersen
Requested Type: Oral
Submitted: 2015-03-13 06:47:55

Co-authors: Mads L. Trolle

Contact Info:
Aalborg University
Skjern 4
Aalborg East,   9220

Abstract Text:
Excitons greatly modify the linear optical response of low-dimensional semiconductors. For cold, clean materials, the response is governed by correlated interband transitions whereas intraband effects vanish. For the second harmonic response, excitons can be equally important. However, mixed intra- and interband transitions are always allowed. In particular, for two-band materials, this is the only non-vanishing contribution. We study theoretically this response in a prototypical low-dimensional, two-band semiconductor: hexagonal boron nitride monolayers. Many-body effects are included via the Bethe-Salpeter equation and we demonstrate how the computation of spectra can be implemented in a highly efficient Green’s function approach. Clear signatures of excitons are observed in both linear and nonlinear response. Hence, predictions for experimental studies are provided.

In the second part of this work, we study intraband effects in electric-field induced second harmonic generation in centrosymmetric low-dimensional semiconductors. We demonstrate how Wannier-Stark states produce a significant second order response. Moreover, highly nonperturbative effects of applied electrostatic fields (second order Franz-Keldysh effect) are observed. Again, clear experimental fingerprints are identified.