Colossal anomalous Stark shift in defect emission of undulated 2D materials

Abstract

We report a strikingly new physical phenomenon that mirror symmetry breaking in undulated two-dimensional (2D) materials induces a colossal Stark shift in defect emissions, occurring without external electric field F, termed anomalous Stark effect. First-principles calculations of multiple defects in bent 2D hBN uncover the fundamental physical reasonings for this anomalous effect and reveal this arises due to strong coupling between flexoelectric polarization and defect dipole moment. This flexo-dipole interaction, similar to that in traditional Stark effect due to F, results in zero-phonon line (ZPL) shifts >500 meV for defects like NBVN and CBVN at $\kappa$ = 1/nm, exceeding typical Stark shifts by 2-3 orders of magnitude. The large ZPL shifts variations with curvature and bending direction offers a method to identify nanotube chirality and explain the large variability in single photon emitters' wavelength in 2D materials, with additional implications for designing nano-electro-mechanical and photonic devices.