Topological spin textures are field arrangements that cannot be continuously deformed to a fully polarized state. In particular, merons are topological textures characterized by half-integer topological charge ±1/2 and vortex-like swirling patterns at large distances. Merons have been studied previously in the context of cosmology, fluid dynamics, condensed matter physics and plasmonics. Here, we visualized optical spin angular momentum of phonon polaritons that resembles nanoscale meron spin textures. Phonon polaritons, hybrids of infrared photons and phonons in hexagonal boron nitride, were excited by circularly polarized light incident on a ring-shaped antenna and imaged using infrared near-field techniques. The polariton field reveals a half-integer topological charge determined by the handedness of the incident beam. Our phonon polaritonic platform opens up new pathways to create, control, and visualize topological textures.
Bibliographical noteFunding Information:
We thank Prof. Andrei Sirenko for fruitful discussions about the mid-IR retarder. Polaritons research at Columbia University and theoretical work at the University of Minnesota are supported by NSF/EFRI-1741660. The development of the scanning probe instrumentation at Columbia University is supported as part of Programmable Quantum Materials, an Energy Frontier Research Center funded by the U.S. Department of Energy (DOE), Office of Science, Basic Energy Sciences (BES), under award DE-SC0019443. D.N.B. is the Vannevar Bush Faculty Fellow ONR-VB: N00014-19-1-2630. D.N.B. is a Moore Investigator in Quantum Materials EPIQS GBMF9455. M.M.F. acknowledges support by the Office of Naval Research under Grant N000014-18-1-2722. The Flatiron Institute is a Division of the Simons Foundation. Support for hBN crystal growth from the Office of Naval Research, award N00014-20-1-2474, is appreciated.
© 2021 American Chemical Society.
- near-field microscopy
- optical vortex
- phonon polariton