Tunable Phonon Polariton Hybridization in a Van der Waals Hetero-Bicrystal

Lukas Wehmeier; Shang-Jie Yu; Xinzhong Chen; Rafael A Mayer; Langlang Xiong; Helen Yao; Yue Jiang; Jenny Hu; Eli Janzen; James H Edgar; Xiaolin Zheng; Tony F Heinz; D N Basov; Christopher C Homes; Guangwei Hu; G Lawrence Carr; Mengkun Liu; Jonathan A Fan

doi:10.1002/adma.202401349

Tunable Phonon Polariton Hybridization in a Van der Waals Hetero-Bicrystal

Adv Mater. 2024 Aug;36(33):e2401349. doi: 10.1002/adma.202401349. Epub 2024 Jun 21.

Authors

Lukas Wehmeier^{1

2}, Shang-Jie Yu³, Xinzhong Chen^{2

4}, Rafael A Mayer², Langlang Xiong⁵, Helen Yao^{6

7}, Yue Jiang⁸, Jenny Hu^{7

9}, Eli Janzen¹⁰, James H Edgar¹⁰, Xiaolin Zheng⁸, Tony F Heinz^{7

9}, D N Basov⁴, Christopher C Homes¹, Guangwei Hu⁵, G Lawrence Carr¹, Mengkun Liu^{1

2}, Jonathan A Fan³

Affiliations

¹ National Synchrotron Light Source II, Brookhaven National Laboratory, Upton, NY, 11973, USA.
² Department of Physics and Astronomy, Stony Brook University, Stony Brook, NY, 11794, USA.
³ Department of Electrical Engineering, Stanford University, Stanford, CA, 94305, USA.
⁴ Department of Physics, Columbia University, New York, NY, 10027, USA.
⁵ Nanyang Technological University, School of Electrical and Electronic Engineering, Singapore, 637371.
⁶ Department of Materials Science and Engineering, Stanford University, Stanford, CA, 94305, USA.
⁷ SLAC National Accelerator Laboratory, Menlo Park, CA, 94025, USA.
⁸ Department of Mechanical Engineering, Stanford University, Stanford, CA, 94305, USA.
⁹ Department of Applied Physics, Stanford University, Stanford, CA, 94305, USA.
¹⁰ Tim Taylor Department of Chemical Engineering, Durland Hall, Kansas State University, Manhattan, KS, 66506, USA.

PMID: 38657644
DOI: 10.1002/adma.202401349

Abstract

Phonon polaritons, the hybrid quasiparticles resulting from the coupling of photons and lattice vibrations, have gained significant attention in the field of layered van der Waals heterostructures. Particular interest has been paid to hetero-bicrystals composed of molybdenum oxide (MoO₃) and hexagonal boron nitride (hBN), which feature polariton dispersion tailorable via avoided polariton mode crossings. In this work, the polariton eigenmodes in MoO₃-hBN hetero-bicrystals self-assembled on ultrasmooth gold are systematically studied using synchrotron infrared nanospectroscopy. It is experimentally demonstrated that the spectral gap in bicrystal dispersion and corresponding regimes of negative refraction can be tuned by material layer thickness, and these results are quantitatively matched with a simple analytic model. Polaritonic cavity modes and polariton propagation along "forbidden" directions are also investigated in microscale bicrystals, which arise from the finite in-plane dimension of the synthesized MoO₃ micro-ribbons. The findings shed light on the unique dispersion properties of polaritons in van der Waals heterostructures and pave the way for applications leveraging deeply sub-wavelength mid-infrared light-matter interactions.

Keywords: metamaterials; nanophotonics; phonon polaritons; synchrotron infrared nanospectroscopy; van der Waals materials.

Abstract

Grants and funding