  New techniques for probing hyperbolic phonon polaritons (HPP) in 2D materials
will support the development of the emerging technologies in this field.
Previous reports have shown that it is possible for WSe2 monolayers in contact
with the hexagonal boron nitride (hBN) to generate HPP in the hBN via Raman
scattering. In this paper, we set out new results on HPP Raman scattering
induced in hBN by WSe2 and MoSe2 monolayers including new resonances at which
the Raman scattering is enhanced. Analysis of the observed Raman lineshapes
demonstrates that Raman scattering allows HPP with wavevectors with magnitudes
significantly in excess of 15000 cm-1 to be probed. We present evidence that
the Raman scattering can probe HPP with frequencies less than the expected
lower bound on the Reststrahlen band suggesting new HPP physics still waits to
be discovered.
