Stanford Advisors

All Publications

  • 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
  • Signatures of moire trions in WSe2/MoSe2 heterobilayers. Nature Liu, E., Barre, E., van Baren, J., Wilson, M., Taniguchi, T., Watanabe, K., Cui, Y., Gabor, N. M., Heinz, T. F., Chang, Y., Lui, C. H. 2021; 594 (7861): 46-50


    Moire superlattices formed by van der Waals materials can support a wide range of electronic phases, including Mott insulators1-4, superconductors5-10 and generalized Wigner crystals2. When excitons are confined by a moire superlattice, a new class of exciton emerges, which holds promise for realizing artificial excitonic crystals and quantum optical effects11-16. When such moire excitons are coupled to charge carriers, correlated states may arise. However, no experimental evidence exists for charge-coupled moire exciton states, nor have their properties been predicted by theory. Here we report the optical signatures of trions coupled to the moire potential in tungsten diselenide/molybdenum diselenide heterobilayers. The moire trions show multiple sharp emission lines with a complex charge-density dependence, in stark contrast to the behaviour of conventional trions. We infer distinct contributions to the trion emission from radiative decay in which the remaining carrier resides in different moire minibands. Variation of the trion features is observed in different devices and sample areas, indicating high sensitivity to sample inhomogeneity and variability. The observation of these trion features motivates further theoretical and experimental studies of higher-order electron correlation effects in moire superlattices.

    View details for DOI 10.1038/s41586-021-03541-z

    View details for PubMedID 34079140

  • Tunable infrared light emission from MoS2/WSe2 heterostructures Karni, O., Barre, E., Lau, S., Gillen, R., Yue, E., Gal, L., Yaffe, T., Kim, B., Watanabe, K., Taniguchi, T., Orenstein, M., Maultzsch, J., Barmak, K., Page, R. H., Heinz, T. F., IEEE IEEE. 2020
  • Infrared Interlayer Exciton Emission in MoS2/WSe2 Heterostructures PHYSICAL REVIEW LETTERS Karni, O., Barre, E., Lau, S., Gillen, R., Ma, E., Kim, B., Watanabe, K., Taniguchi, T., Maultzsch, J., Barmak, K., Page, R. H., Heinz, T. F. 2019; 123 (24)
  • Spatial Separation of Carrier Spin by the Valley Hall Effect in Monolayer WSe2 Transistors. Nano letters Barre, E., Incorvia, J. A., Kim, S. H., McClellan, C. J., Pop, E., Wong, H. P., Heinz, T. F. 2019


    We investigate the valley Hall effect (VHE) in monolayer WSe2 field-effect transistors using optical Kerr rotation measurements at 20 K. While studies of the VHE have so far focused on n -doped MoS2, we observe the VHE in WSe2 in both the n - and p -doping regimes. Hole doping enables access to the large spin-splitting of the valence band of this material. The Kerr rotation measurements probe the spatial distribution of the valley carrier imbalance induced by the VHE. Under current flow, we observe distinct spin-valley polarization along the edges of the transistor channel. From analysis of the magnitude of the Kerr rotation, we infer a spin-valley density of 44 spins/mum, integrated over the edge region in the p -doped regime. Assuming a spin diffusion length less than 0.1 mum, this corresponds to a spin-valley polarization of the holes exceeding 1%.

    View details for PubMedID 30601667

  • Infrared Interlayer Exciton Emission in MoS_{2}/WSe_{2} Heterostructures. Physical review letters Karni, O. n., Barré, E. n., Lau, S. C., Gillen, R. n., Ma, E. Y., Kim, B. n., Watanabe, K. n., Taniguchi, T. n., Maultzsch, J. n., Barmak, K. n., Page, R. H., Heinz, T. F. 2019; 123 (24): 247402


    We report light emission around 1 eV (1240 nm) from heterostructures of MoS_{2} and WSe_{2} transition metal dichalcogenide monolayers. We identify its origin in an interlayer exciton (ILX) by its wide spectral tunability under an out-of-plane electric field. From the static dipole moment of the state, its temperature and twist-angle dependence, and comparison with electronic structure calculations, we assign this ILX to the fundamental interlayer transition between the K valleys in this system. Our findings gain access to the interlayer physics of the intrinsically incommensurate MoS_{2}/WSe_{2} heterostructure, including moiré and valley pseudospin effects, and its integration with silicon photonics and optical fiber communication systems operating at wavelengths longer than 1150 nm.

    View details for DOI 10.1103/PhysRevLett.123.247402

    View details for PubMedID 31922842