Abstract
The confinement of electromagnetic radiation to subwavelength scales relies on strong light–matter interactions. In the infrared and terahertz spectral ranges, phonon polaritons are commonly employed to achieve deeply subdiffractional light confinement, with such optical modes offering much lower losses in comparison to plasmon polaritons. Among these, hyperbolic phonon polaritons in anisotropic materials offer a promising platform for light confinement. Here we report on ultraconfined phonon polaritons in hafnium-based dichalcogenides with confinement factors exceeding λ0/250 in the terahertz spectral range. This extreme light compression within deeply subwavelength thin films is enabled by the large magnitude of the light–matter coupling strength in these compounds and the natural hyperbolicity of HfSe2. Our findings emphasize the role of light–matter coupling for polariton confinement, which for phonon polaritons in polar dielectrics is dictated by the transverse–longitudinal optical phonon energy splitting. Our results demonstrate transition-metal dichalcogenides as an enabling platform for terahertz nanophotonic applications.
| Original language | English |
|---|---|
| Pages (from-to) | 1735-1741 |
| Number of pages | 7 |
| Journal | Nature Materials |
| Volume | 24 |
| Issue number | 11 |
| DOIs | |
| State | Published - Nov 2025 |
Funding
R.A.K. acknowledges that this work was supported by a NASA Space Technology Graduate Research Opportunity. N.S.M. acknowledges funding from the Deutsche Forschungsgemeinschaft (German Research Foundation; project 551280726). K.D.-G. was supported by the Army Research Office (grant W911NF-21-1-0119). A.S. acknowledges support from the Department of Energy, Basic Energy Sciences (grant DE-FG02-09ER4655). S.D. and J.D.C. were supported by the Office of Naval Research MURI on Twist-Optics (grant N0001-23-1-2567). P.A.-G. acknowledges support from the European Research Council (consolidator grant 101044461, TWISTOPTICS) and the Spanish Ministry of Science and Innovation (State Plan for Scientific and Technical Research and Innovation grant PID2022-141304NB-I00). M.O., F.G.K., J.W., L.M.E. and S.C.K. acknowledge financial support from the Bundesministerium für Bildung und Forschung (Federal Ministry of Education and Research, Germany, project grants 05K19ODB and 05K22ODA) and from the Deutsche Forschungsgemeinschaft under Germany’s Excellence Strategy through the Würzburg-Dresden Cluster of Excellence on Complexity and Topology in Quantum Matter—ct.qmat (grant EXC 2147, project 390858490) and through the Collaborative Research Center on Chemistry of Synthetic Two-Dimensional Materials (CRC1415, 417590517). The Au discs were fabricated as part of a user project at the Center for Nanophase Materials Sciences, which is a US Department of Energy, Office of Science User Facility at Oak Ridge National Laboratory. Open access funding provided by Max Planck Society.