Tightly bound Suris tetrons in monolayer black phosphorus from first principles.

Suris tetrons are multiparticle excitations that emerge as a result of the interaction of an exciton with the Fermi surface in doped semiconductors. We present the first ab initio calculation of Suris tetron, giving us a unique opportunity to study the character of such excitations in detail. In this work, we compute Fermi polarons through an interacting, four-particle state within the picture of a Suris tetron, focusing on monolayer black phosphorus (BP). In particular, we will describe the Suris tetron as a tightly bound exciton coupled with Fridel oscillations. This coupling plays an important role in building correlation and increasing the binding energy of such excitations compared to the description from an interacting three-particle formalism (e.g., a trion). Additionally, we elaborate on the computational method we used to achieve fast convergence of the excited state based on an efficient Lanczos scheme. This work addresses the impact of four-particle formalism in capturing the essential physics of excited states in doped semiconductors and resolves previous disagreements between experimentally deduced and theoretically predicted binding energies of charged excitons in BP.