Direct observation of massless excitons and linear exciton dispersion
ORAL
Abstract
Excitons in two-dimensional (2D) materials provide a unique platform for exploring many-body physics. In this work, we report the first direct observation of linearly dispersive, massless excitons in freestanding monolayer hexagonal boron nitride (hBN) using momentum-resolved electron energy-loss spectroscopy (Q-EELS). The measured exciton group velocity of 8×10^5 m/s shows excellent agreement with ab initio GW-BSE theory, and the lowest dipole-allowed transition is identified at 6.6 eV, resolving a long-standing debate on the band gap of monolayer hBN. These results provide unambiguous evidence of massless excitons in a 2D material and establish momentum-resolved EELS as a powerful probe of exciton band structure, opening new opportunities for studying excitonic transport and collective quantum phases.
*This work was made possible through the support of the Enrico Fermi Fellowships led by the Center for Spacetime and the Quantum, and supported by Grant ID #63132 from the John Templeton Foundation. The opinions expressed in this publication are those of the author(s) and do not necessarily reflect the views of the John Templeton Foundation or those of the Center for Spacetime and the Quantum.
–
Publication: arXiv:2502.20454
Presenters
-
Luna Y. Liu
- Yale University