Rational Design of Point Defects With Small Electron-Phonon Coupling in 2D Materials

Point defects in semiconductors have emerged as an attractive candidate for applications in quantum information science. Due to their ability to create well-localized states within the band gap, point defects can serve as effectively isolated atoms that can be utilized as single photon emitters (SPEs) and qubits.

Photon-indistinguishability is a key factor that determines the suitability of defect systems as SPEs, which is often quantified by small Huang-Rhys (HR) factors. Not only is the computation of HR factors challenging, but once computed, they are frequently employed merely as a score without any attempts to establish a meaningful connection between HR factors and the physical defect system.



We propose that small HR factors are linked to the preservation of bonding character between the initial (occupied) and final (unoccupied) states involved in a specific transition. Establishing this association would enable the development of a rational design principle for defects that target small HR factors. We demonstrate this principle for realistic SPEs candidates in hBN defect systems. HR factors are first calculated through first-principles employing the one-dimensional configuration coordinate diagram (1DCCD) approximation, then compared with full calculations involving phonon spectra, where we carefully extrapolate spectral functions towards the dilute defect limit. Calculated HR factors are then related to the degree of bonding-character similarity between excited and ground states.