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On the validity of the Franck-Condon principle in the optical spectroscopy: optical conductivity of the Fröhlich polaron

G. De Filippis·V. Cataudella·A. S. Mishchenko·C. A. Perroni·J. T. Devreese
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Abstract

The optical absorption of the Fröhlich polaron model is obtained by an approximation-free Diagrammatic Monte Carlo method and compared with two new approximate approaches that treat lattice relaxation effects in different ways. We show that: i) a strong coupling expansion, based on the the Franck-Condon principle, well describes the optical conductivity for large coupling strengths ($α>10$); ii) a Memory Function Formalism with phonon broadened levels reproduces the optical response for weak coupling strengths ($α<6$) taking the dynamic lattice relaxation into account. In the coupling regime $6<α<10$ the optical conductivity is a rapidly changing superposition of both Franck-Condon and dynamic contributions.

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G. De Filippis, V. Cataudella, A. S. Mishchenko, C. A. Perroni, J. T. Devreese. 2006-03-08. On the validity of the Franck-Condon principle in the optical spectroscopy: optical conductivity of the Fröhlich polaron. https://doi.org/10.1103/physrevlett.96.136405

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