Wigner solid of charge transfer excitons in Yin-Yang Kagome lattice*

We demonstrate that photo absorption between two enantiomorphic topological flat bands, as hosted in a Yin-Yang Kagome lattice, provides a perfect platform for the realization of excitonic Wigner crystallization. By solving the Bethe Salpeter equation in Tamm Dancoff approximation within a tight-binding framework, we study the flat-band excitons in terms of their binding energy and dispersion. We show that they are charge-transfer excitons, characterized by a constant binding energy (dispersion-less) in momentum space and highly localized electron-hole pair distribution function in real space. By virtue of electronic and excitonic flat bands our results are indicative of excitonic Wigner crystallization. This would be the first-time realization of Wigner solid of charge-transfer excitons in a lattice model. Our findings open the door to further investigation of photo excitation and many-body physics of correlated electrons in multiple flat bands.