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Solid-state single-photon emitters (SPEs) such as the bright, stable, room-temperature defects within hexagonal boron nitride (hBN) are of increasing interest for quantum information science. To date, the atomic and electronic origins of SPEs within hBN have not been well understood, and no studies have reported photochromism or explored cross correlations between hBN SPEs. Here, we combine irradiation time-dependent microphotoluminescence spectroscopy with two-color Hanbury Brown–Twiss interferometry in an investigation of the electronic structure of hBN defects. We identify evidence of photochromism in an hBN SPE that exhibits single-photon cross correlations and correlated changes in the intensity of its two zero-phonon lines. 

Abstract PdSe₂, an emerging 2D material with a novel anisotropic puckered pentagonal structure, has attracted growing interest due to its layer‐dependent electronic bandgap, high carrier mobility, and good air stability. Herein, a detailed Raman spectroscopic study of few‐layer PdSe₂(two to five layers) under the in‐plane uniaxial tensile strain up to 3.33% is performed. Two of the prominent PdSe₂Raman peaks are influenced differently depending on the direction of strain application. The mode redshifts more than the mode when the strain is applied along thea‐axis of the crystal, while the mode redshifts more than the mode when the strain is applied along theb‐axis. Such an anisotropic phonon response to strain indicates directionally dependent mechanical and thermal properties of PdSe₂and also allows the identification of the crystal axes. The results are further supported using first‐principles density‐functional theory. Interestingly, the near‐zero Poisson’s ratios for few‐layer PdSe₂are found, suggesting that the uniaxial tensile strain can easily be applied to few‐layer PdSe₂without significantly altering their dimensions at the perpendicular directions, which is a major contributing factor to the observed distinct phonon behavior. The findings pave the way for further development of 2D PdSe₂‐based flexible electronics.