Dimensionality transitions of exciton Fano resonance spectra in a semiconductor Wannier-Stark ladder

The dimensionality transition revealed by modulations of exciton Fano resonance (FR) spectra in a semiconductor Wannier-Stark ladder with respect to an applied static electric field is traced by use of calculated spectra based on the multichannel scattering theory. With decreasing the bias, marked overlap resonance between adjacent FR profiles causes contrastive modulation patterns of the spectra in two distinct regions of a photon energy E below and above the Van Hove M0 critical point εM0 of the original superlattices. By coalescence of a great number of fine spectra with very narrow widths, the structured continuum spectra of the exciton FR in the region of E<εM0 are transformed into a sharp peak of a pure bound state. On the other hand, by coalescence of a great number of structureless continua, those in the region of E>εM0 are transformed into a broad plateau.