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Self-Trapped Exciton Defects in a Charge Density Wave: Electronic Excitations of BaBiO3

Philip B. Allen·Ilka B. Bischofs
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Abstract

In the previous paper, it was shown that holes doped into BaBiO3 self-trap as small polarons and bipolarons. These point defects are energetically favorable partly because they undo locally the strain in the charge-density-wave (Peierls insulator) ground state. In this paper the neutral excitations of the same model are discussed. The lowest electronic excitation is predicted to be a self-trapped exciton, consisting of an electron and a hole located on adjacent Bi atoms. This excitation has been seen experimentally (but not identified as such) via the Urbach tail in optical absorption, and the multi-phonon spectrum of the ``breathing mode'' seen in Raman scattering. These two phenomena occur because of the Franck-Condon effect associated with oxygen displacement in the excited state.

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Philip B. Allen, Ilka B. Bischofs. 2001-08-05. Self-Trapped Exciton Defects in a Charge Density Wave: Electronic Excitations of BaBiO3. https://doi.org/10.1103/physrevb.65.115113

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