Correlated multi-particle excitations: Green’s function formalism for trions and biexcitons*

With the experimental isolation of atomically thin one- and two-dimensional materials, it is now possible to measure a variety of charged and neutral multiparticle excitations (trions, biexcitons, etc.) in these systems, many of which display large binding energies. On the theory side, however, while quasiparticle and neutral optical excitations have been successfully treated in many materials with the first-principles GW and GW plus Bethe-Salpeter equation (GW-BSE) approaches, respectively, similar many-body and parameter-free approaches are not available to compute and understand correlated multi-particle excitations. Accordingly, past theoretical studies were often limited to treatments based on model Hamiltonians. In this talk, we present results from a new ab initio approach based on the interacting 3- and 4-particle Green’s function formalism to compute multiparticle excitations [1]. Our new diagrammatic approach that makes use of appropriate screened Coulomb interactions, combined with a high-performance computing implementation, allows us to predict without adjustable parameters that trions and biexcitons in carbon nanotubes are stable at room temperature, and also to reveal in details electronic correlation in these multiparticle excitations. We will also comment on how this formalism can be employed to investigate other high-order excited-state phenomena in the bulk and at the nanoscale.

[1] F. H. da Jornada, A. Cepellotti, and S. G. Louie, submitted.