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

TL;DR

This paper investigates quasi-bound electron pairs in two-dimensional materials with Mexican-hat dispersion, revealing unique formation mechanisms and conditions under which these states can become bound states in the continuum.

Contribution

It introduces the concept of quasi-bound electron pairs in MHD materials and analyzes their formation, especially in topological insulators with hybridized bands.

Findings

Resonance width can vanish, transforming quasi-bound states into bound states in continuum.

Weak hybridization leads to extremely small resonance widths.

Singlet pairs with zero angular momentum have the highest binding energy.

Abstract

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