Stanford Advisors

All Publications

  • Optical absorption of interlayer excitons in transition-metal dichalcogenide heterostructures. Science (New York, N.Y.) Barre, E., Karni, O., Liu, E., O'Beirne, A. L., Chen, X., Ribeiro, H. B., Yu, L., Kim, B., Watanabe, K., Taniguchi, T., Barmak, K., Lui, C. H., Refaely-Abramson, S., da Jornada, F. H., Heinz, T. F. 2022; 376 (6591): 406-410


    Interlayer excitons, electron-hole pairs bound across two monolayer van der Waals semiconductors, offer promising electrical tunability and localizability. Because such excitons display weak electron-hole overlap, most studies have examined only the lowest-energy excitons through photoluminescence. We directly measured the dielectric response of interlayer excitons, which we accessed using their static electric dipole moment. We thereby determined an intrinsic radiative lifetime of 0.40 nanoseconds for the lowest direct-gap interlayer exciton in a tungsten diselenide/molybdenum diselenide heterostructure. We found that differences in electric field and twist angle induced trends in exciton transition strengths and energies, which could be related to wave function overlap, moire confinement, and atomic reconstruction. Through comparison with photoluminescence spectra, this study identifies a momentum-indirect emission mechanism. Characterization of the absorption is key for applications relying on light-matter interactions.

    View details for DOI 10.1126/science.abm8511

    View details for PubMedID 35446643

  • Structure of the moire exciton captured by imaging its electron and hole. Nature Karni, O., Barre, E., Pareek, V., Georgaras, J. D., Man, M. K., Sahoo, C., Bacon, D. R., Zhu, X., Ribeiro, H. B., O'Beirne, A. L., Hu, J., Al-Mahboob, A., Abdelrasoul, M. M., Chan, N. S., Karmakar, A., Winchester, A. J., Kim, B., Watanabe, K., Taniguchi, T., Barmak, K., Madeo, J., da Jornada, F. H., Heinz, T. F., Dani, K. M. 2022; 603 (7900): 247-252


    Interlayer excitons (ILXs) - electron-hole pairs bound across two atomically thin layered semiconductors - have emerged as attractive platforms to study exciton condensation1-4, single-photon emission and other quantum information applications5-7. Yet, despite extensive optical spectroscopic investigations8-12, critical information about their size, valley configuration and the influence of the moire potential remains unknown. Here, in a WSe2/MoS2 heterostructure, we captured images of the time-resolved and momentum-resolved distribution of both of the particles that bind to form the ILX: the electron and the hole. We thereby obtain a direct measurement of both the ILX diameter of around 5.2nm, comparable with the moire-unit-cell length of 6.1nm, and the localization of its centre of mass. Surprisingly, this large ILX is found pinned to a region of only 1.8nm diameter within the moire cell, smaller than the size of the exciton itself. This high degree of localization of the ILX is backed by Bethe-Salpeter equation calculations and demonstrates that the ILX can be localized within small moire unit cells. Unlike large moire cells, these are uniform over large regions, allowing the formation of extended arrays of localized excitations for quantum technology.

    View details for DOI 10.1038/s41586-021-04360-y

    View details for PubMedID 35264760

  • Light Absorption and Emission Dominated by Trions in the Type-I van der Waals Heterostructures ACS PHOTONICS Bae, H., Kim, S., Lee, S., Noh, M., Karni, O., O'Beirne, A. L., Barre, E., Sim, S., Cha, S., Jo, M., Heinz, T. F., Choi, H. 2021; 8 (7): 1972-1978