Although THz technology promises fast data processing, integration into compact devices has been a challenge due to its long wavelength. Traditional materials had difficulty compressing THz light effectively, limiting the potential for miniaturization.
To address this, the research team used hafnium dichalcogenides, a type of layered material composed of hafnium and chalcogen elements such as sulfur or selenium. By using phonon polaritons (a type of quasiparticle that results from the coupling of light with lattice vibrations in a crystal), they achieved extreme compression of THz light by compressing the THz wavelengths from over 50 micrometers in length to dimensions of less than 250 nanometers. This was achieved with minimal energy loss and paves the way for more energy-efficient THz devices. One collaborator, Artem Mishchenko, put this progress in excellent context by comparing the over 200-fold compression of light waves to the confinement of ocean waves in a teacup, Caldwell noted.
The teams’ collaboration focused on understanding how light and matter interact at the nano- to atomic-scale, their impact on nonlinear optics, and how such changes differ from bulk materials. This includes the subdiffractional focusing of light using polaritons in the optical spectral region (primarily in the infrared), the design of nanoscale optical components, and the identification and characterization of novel optical, electro-optical and electronic materials.
“This began as a summer research project for a student, but quickly evolved into an exciting observation of an unprecedented level of optical compression,” Caldwell said.
The study grew out of a long-standing collaboration between the Berlin-based FHI, Vanderbilt and TU Dresden, using the Near-Field Optical Microscope installed by the Eng group at the Free-Electron Laser User Facility FELBE at the Helmholtz-Zentrum Dresden-Rossendorf (HZDR), Germany. This microscope has been developed and maintained over the past 15 years in close collaboration between TU Dresden and the HZDR as a user laboratory. “Exploring ultra-high THz light compression by phonon polaritons, e.g. in hafnium dichalcogenides, requires the extreme nanoscale imaging capabilities of our near-field microscope at the HZDR free-electron laser,” said Lukas Eng from TU Dresden.
The results could lead to the development of ultra-compact THz resonators and waveguides, which are essential for applications in environmental sensing and security imaging. The integration of these materials into van der Waals heterostructures (structures formed by stacking layers of two-dimensional materials with weak vertical interactions) could further enhance the capabilities of 2D materials research and provide new opportunities for nanoscale optoelectronic integration.
The researchers said the study not only highlights hafnium dichalcogenides as a promising platform for THz applications, but also sets the stage for exploring new physics through ultra-strong or even deep-strong light-matter coupling. The results point to a future where high-throughput materials screening could identify even more effective materials for THz technology, driving innovation in this critical area.
“Our work with hafnium dichalcogenides shows how we can push the boundaries of THz technology, potentially transforming the way we approach optoelectronic integration,” said Paarmann of the Fritz Haber Institute.
Original publication:
Kowalski, R.A., Mueller, N.S., Álvarez-Pérez, G. et al. Ultraconfined terahertz phonon polaritons in hafnium dichalcogenides. Nat. Mater. (2025). https://doi.org/10.1038/s41563-025-02345-0
Contact:
Prof. Lukas Eng
TU Dresden, Professur für Experimentalphysik/Photophysik
E-Mail: lukas.eng@tu-dresden.de
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Further links
👉 https://tu-dresden.de
Photo: Ryan Kowalski and Niclas Müller
