Center for Functional Nanomaterials Seminar

Excitonic effects in ideal 1D systems are known to show very peculiar features. However, the occurrence of such effects in real systems is far from being obvious. Besides, the relevance of Coulomb interactions can strongly depend on the specific system. We present the main characteristics of optical excitations in semiconductor nanotubes, as obtained from accurate ab-initio many-body calculations, and compare them with other quasi-one-dimensional semiconducting systems. Our theoretical approach, which includes both self-energy corrections and excitonic effects through the GW-BSE formalism, can provide a deep understanding of excited-state properties. In all the studied cases, excitonic effects play a crucial role, with tightly bound excitons dominanting the spectra. Within the same formalism, we first compute two-photon absorption spectra, achieving excellent agreement with recent experiments. Moreover, a complete symmetry analysis of the excitonic states is carried out, fundamental for understanding the luminescence features observed in experiments.