Temperature Dependence of Wavelength Selectable Zero-Phonon Emission   from Single Defects in Hexagonal Boron Nitride
  We investigate the distribution and temperature-dependent optical properties of sharp, zero-phonon emission from defect-based single photon sources in multilayer hexagonal boron nitride (h-BN) flakes. We observe sharp emission lines from optically active defects distributed across an energy range that exceeds 500 meV. Spectrally-resolved photon-correlation measurements verify single photon emission, even when multiple emission lines are simultaneously excited within the same h-BN flake. We also present a detailed study of the temperature-dependent linewidth, spectral energy shift, and intensity for two different zero-phonon lines centered at 575 nm and 682 nm, which reveals a nearly identical temperature dependence despite a large difference in transition energy. Our temperature-dependent results are best described by a lattice vibration model that considers piezoelectric coupling to in-plane phonons. Finally, polarization spectroscopy measurements suggest that whereas the 575 nm emission line is directly excited by 532 nm excitation, the 682 nm line is excited indirectly. 
Nicholas R. Jungwirth, Brian Calderon, Yanxin Ji, Michael G. Spencer,   Michael E. Flatt\'e, and Gregory D. Fuchs
cond-mat.mtrl-sci cond-mat.mes-hall quant-ph