Low‐Loss Anisotropic Image Polaritons in van der Waals Crystal α‐MoO3. Issue 21 (6th September 2022)

• Record Type: Journal Article
• Authors: Menabde, Sergey G.; Jahng, Junghoon; Boroviks, Sergejs; Ahn, Jongtae; Heiden, Jacob T.; Hwang, Do Kyung; Lee, Eun Sung; Mortensen, N. Asger; Jang, Min Seok
• Is Part Of: Advanced optical materials. Volume 10:Issue 21(2022)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2022-09-06
• Subjects: image polaritons -- phonon‐polaritons -- van der Waals crystals; Optical materials -- Periodicals; Photonics -- Periodicals; 620.11295
• DOI: 10.1002/adom.202201492
• Languages: English
• ISSNs: 2195-1071

Abstract

Abstract: Orthorhombic molybdenum trioxide (α‐MoO3 ), a newly discovered polaritonic van der Waals crystal, is attracting significant attention due to its strongly anisotropic mid‐infrared phonon‐polaritons. At the same time, coupling of polariton with its mirror image in an adjacent metal gives rise to a significantly more confined image mode. Here, monocrystalline gold flakes—an atomically flat low‐loss substrate for mid‐infrared image polaritons—are employed to measure the full complex‐valued propagation constant of the hyperbolic image phonon‐polaritons in α‐MoO3 by near‐field probing. The anisotropic dispersion is mapped and the damping of the polaritons propagating at different angles to the crystallographic directions of α‐MoO3 is analyzed. These experiments demonstrate the strongly confined image phonon‐polaritons in α‐MoO3 exhibiting intrinsic limiting lifetime of 4.2 ps and a propagation length of 4.5 times the polariton wavelength, owing to the negligible substrate‐mediated loss. Furthermore, it is shown that the image modes with positive group velocity have simultaneously larger momentum and lifetime compared to their counterparts on a dielectric substrate, while the image modes with negative group velocity possess a smaller momentum. These results spotlight the hyperbolic image phonon‐polaritons as a superior platform for unconventional light manipulation at the nanoscale. Abstract : Hyperbolic image phonon‐polaritons in α‐MoO3 on monocrystalline gold demonstrate simultaneously longer lifetime and larger field compression, providing a new platform for light manipulation at nanoscale. Besides, monocrystalline gold flakes are demonstrated to be a superior substrate for near‐field studies of phonon‐polaritons in van der Waals crystals.