Quasi-bound Electron Pairs in Two-Dimensional Materials with a Mexican-Hat Dispersion

We study quasi-bound states of two electrons that arise in two-dimensional materials with a Mexican-hat dispersion (MHD) at an energy above its central maximum. The width the resonance local density created by pairs is determined hybridization atomic orbitals, due to which MHD formed. mechanism state formation fact effective reduced mass near top negative. An unusual feature can vanish and then they transform into bound continuum. detail for topological insulators, when inverted electron hole bands. In this case, extremely small weak hybridization. highest binding achieved singlet zero angular number.