Temperature Dependence of Wavelength Selectable Zero-Phonon Emission from Single Defects in Hexagonal Boron Nitride (1605.04445v1)

Abstract: 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.

• The paper reports a diverse zero-phonon emission spectrum spanning over 500 meV, confirming multiple defect types in h-BN.
• The study uses high-resolution and polarization spectroscopy to uncover temperature-dependent broadening and red-shifting in 575 nm and 682 nm ZPLs.
• The findings suggest promising applications in quantum photonics and strain-engineered defect control in 2D materials.

Temperature Dependence of Zero-Phonon Emission in Hexagonal Boron Nitride

This paper investigates the temperature-dependent optical characteristics of point defects in multilayer hexagonal boron nitride (h-BN), focusing specifically on zero-phonon emission lines (ZPLs). By characterizing emissions from individual defects across a wide energy spectrum, the paper provides insights into the intricate interplay between defect states and the lattice environment in 2D materials.

Key Findings

The authors have reported several critical observations about the emission lines in h-BN:

• Diverse ZPL Spectrum: The narrow spectral lines identified cover an energy range exceeding 500 meV, indicating the presence of multiple optically active defect types within the h-BN lattice.
• Temperature-Dependent Phenomena: For ZPLs centered at 575 nm and 682 nm, the paper reveals analogous temperature-dependent broadening and red-shifting patterns, despite substantial differences in their transition energies.
• Phonon Interactions: The results are best explained by a model involving phonon interactions that suggest piezoelectric coupling to in-plane phonons. The broadening of emission lines with temperature is consistent with phonon-mediated mechanisms.
• Polarization Spectroscopy: Distinct polarization behaviors for the two studied ZPLs hint at different excitation mechanisms—direct excitation for the 575 nm ZPL and indirect excitation for the 682 nm ZPL via cross relaxation.

Methodological Approach

Using high-resolution spectroscopy, the authors identify and analyze multiple sharp emission lines from h-BN flakes at cryogenic temperatures. Photon-correlation measurements are employed to confirm single-photon emission characteristics. The paper also leverages polarization spectroscopy to further unravel the nature of the defects and their interactions with incident light.

Implications

The analysis of ZPLs in h-BN speaks to both theoretical ambitions and practical applications:

• Quantum Optics and Information Technology: The stability and brightness of ZPL emissions in h-BN make it a promising candidate material for applications in quantum optics and quantum information processing, where single-photon sources are crucial.
• Defect Dynamics: The paper's findings regarding phonon interactions contribute to the understanding of defect dynamics in the 2D material framework, expanding theoretical models traditionally used for 3D defect systems.
• Strain and Defect Engineering: The coupling of emissions to local lattice strains implies potential for defect engineering through controlled strain application, which could tailor defect properties for desired functionalities.

Future Prospects

The outcomes highlight several avenues for further research:

• Defect Identification: Detailed identification of individual defect species could provide a more comprehensive understanding of their electronic structures and interactions.
• Temperature-Dependent Models: Continued refinement of phonon-mediated linewidth broadening models can offer precise predictions for other 2D material systems.
• Enhancement of Photostability: The paper suggests that surface treatments might improve the photostability of defects in monolayer variants, which could extend the practical utility of h-BN as a photonic material.

In synthesizing these results, the paper significantly advances our understanding of defect-based photonics in layered materials and primes h-BN as a robust platform for next-generation optical technologies.