Theory of single and double electron spin-flip Raman scattering in semiconductor nanoplatelets

TL;DR

This paper develops a comprehensive theory of electron spin-flip Raman scattering in semiconductor nanoplatelets, explaining spectral shifts, polarization properties, and the roles of various intermediate states, with validation against experimental data.

Contribution

It introduces a new theoretical framework for understanding spin-flip Raman scattering in nanoplatelets, emphasizing the role of exciton-electron complexes over trion states.

Findings

Resonant scattering involves exciton plus localized electrons rather than trions.

Identifies an indirect scattering channel involving hole and electron localization.

Theoretical predictions align with recent experimental observations.

Abstract

A theory of electron spin-flip Raman scattering (SFRS) is presented that describes the Raman spectral signals shifted by both single and twice the electron Zeeman energy under nearly resonant excitation of the heavy hole excitons in semiconductor nanoplatelets. We analyze the spin structure of photoexcited intermediate states, derive compound matrix elements of the spin-flip scattering and obtain polarization properties of the one- and two-electron SFRS common for all the intermediate states. We show that, in the resonant scattering process under consideration, the complexes "exciton plus localized resident electrons" play the role of main intermediate states rather than tightly bound trion states. It is demonstrated that, in addition to the direct photoexcitation (and similar photorecombination) channel, there is another indirect channel contributing to the SFRS process. In the indirect channel, the photohole forms the exciton state with the resident electron removed from the localization site while the photoelectron becomes localized on this site. The theoretical results are compared with recent experimental findings for ensembles of CdSe nanoplatelets.