The effect of electron-phonon interactions on the spectral properties of single defects in hBN.
We investigate the temperature dependent spectral properties of a single defect in hexagonal boron nitride (hBN). We observe a sharp zero-phonon line (ZPL) emission accompanied by Stokes and anti-Stokes optical phonon sidebands assisted by the Raman active low-energy ($\approx~6.5$ meV) interlayer shear mode of hBN. The spectral lineshape around the ZPL is measured down to 78 K, where the linewidth of the ZPL is measured as 172 $\mu$eV. By employing a quadratic electron-phonon interaction, the temperature dependent broadening and the lineshift of the ZPL are found to follow $T+T^5$ and $T+T^3$ dependence, respectively. Furthermore, the temperature dependent lineshape around the ZPL is modeled with a linear electron-phonon coupling theory, which allowed us to calculate the Debye-Waller factor as 0.59.