Decoding Imperfections in Hexagonal Boron Nitride for Quantum Applications
September 30, 2024

Single-photon emission process in layered hBN. Upon excitation on a defect site, electrons can recombine optically with other defects at a distance of a few atomic site and emit single photons. Credit: Nat. Mater. (2024).
The Science
Scientists uncover an elementary excitation in hexagonal Boron Nitride (hBN) that triggers a range of harmonic electronic states correlated with single-photon emitters (SPEs).
The Impact
A more complete understanding of SPEs in materials like hBN could lead to breakthroughs in quantum applications like quantum computing, sensing, cryptography, and simulations.
Summary
Single-photon emitters (SPEs), materials that can produce one single particle of light at a time, have become a key component in new technologies in the field of quantum photonics. Recent research has found bright, adjustable, and stable emitters in a material called hexagonal boron nitride (hBN), which could be used across a wide range of light wavelengths. While it's known that defects in hBN create these emitters, little is known about how these defects work and their origin. In this study, researchers used advanced techniques to uncover key energy levels in hBN that are linked to single-photon emitters. They also pinpoint the atomic orbitals involved in the generation of single photon emission. This finding offers new insights into how quantum light emission works in materials like hBN and could lead to further discoveries in other materials.
Prior research was unable to provide a clear, microscopic picture of the energy levels of defects leading to single photon emission in hBN. To look at hBN in a new way and gain this necessary perspective, the team combined photoluminescence (PL) spectroscopy with resonant inelastic X-ray scattering (RIXS), a technique sensitive to elementary electronic excitations. They were able to perform the latter technique using the Soft Inelastic X-ray Scattering (SIX) beamline at the National Synchrotron Light Source II (NSLS-II), a U.S. Department of Energy (DOE) Office of Science User Facility at DOE’s Brookhaven National Laboratory and a state-of-the-art instrument in the field. RIXS measures the elementary excitations, and therefore the energy level of a system, by exciting the core electrons in a material into an intermediate state that relaxes into an excited state releasing a photon in the process. This allows scientists to study different types of electronic activity, such as spin, charge, and lattice vibrations on very small samples with high precision.
When examining hBN with RIXS, the team found that at specific X-ray energies, they could observe different responses. For pure hBN samples with no or low amounts of defects, RIXS did not detect any states related to SPEs. In hBN treated to create defects, single-photon emitters were detected with an elementary energy of 285 meV. This fundamental energy level produces a series of harmonics covering a wide range of light, from mid-infrared to ultraviolet. This matched up with the single-photon emitters seen in the visible light range when using PL spectroscopy. These harmonics are linked to specific electronic transitions in hBN, revealing new details about the material’s electronic structure, and correlate with the energies of SPEs observed across several other experiments conducted worldwide. By understanding how to distinguish between different types of electronic and vibrational activities in hBN, scientists gain insight into how defects affect its light-emitting properties, furthering a more complete and microscopic understanding of not only hBN but other kinds of photonic quantum materials. These materials can one day play a role in controlling quantum states in quantum technologies like quantum computing, communication, simulation, cryptography and more.
Download the research summary slide (PDF)
Contact
Jonathan Pelliciari
Brookhaven National Laboratory
pelliciari@bnl.gov
Gabriele Grosso
City University of New York
ggrosso@gc.cuny.edu
Publications
Pelliciari J, Mejia E, Woods JM, Gu Y, Li J, Chand SB, Fan S, Watanabe K, Taniguchi T, Bisogni V, Grosso G. Elementary excitations of single-photon emitters in hexagonal boron nitride. Nature Materials (2024). https://doi.org/10.1038/s41563-024-01866-4
Funding
Work at Brookhaven National Laboratory was supported by the US Department of Energy (DOE) Office of Science under contract no. DE-SC0012704 (J.P., Y.G., J.L., S.F. and V.B.). This work was also supported by the Laboratory Directed Research and Development project of Brookhaven National Laboratory No. 21-037 (J.P. and S.F.) and by the US DOE Office of Science, Early Career Research Program (V.B. and Y.G). This research used Beamline 2-ID of the National Synchrotron Light Source II, a US DOE Office of Science User Facility, operated for the DOE Office of Science by Brookhaven National Laboratory under contract no. DE-SC0012704. Work at CUNY is supported by the National Science Foundation (NSF) (grant no. DMR-2044281) (G.G.), the physics department of the Graduate Center of CUNY and the Advanced Science Research Center (E.M., J.M.W., S.B.C. and G.G.) and the Research Foundation through PSC-CUNY award no. 64510-00 52 (G.G.). K.W. and T.T. acknowledge support from the Elemental Strategy Initiative conducted by MEXT, Japan (grant no. JPMXP0112101001), and JSPS KAKENHI (grant nos. 19H05790, 20H00354 and 21H05233).
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