Nanoscale mapping and spectroscopy of non-radiative hyperbolic modes in hexagonal boron nitride nanostructures

Published: March 14, 2018

Author(s)

Lisa Brown, Marcelo I. Davanco, Zhiyuan Sun, Andrey Kretinin, Yiguo Chen, Joseph Matson, Igor Vurgaftman, Nicholas Sharac, Alexander Giles, Michael Fogler, Takashi Taniguchi, Kenji Watanabe, Kostya Novoselov, Stefan Maier, Andrea Centrone, Joshua D. Caldwell

Abstract

Because of its inherent crystal anisotropy, hexagonal boron nitride (hBN) supports naturally hyperbolic phonon polaritons, i.e. polaritons that can propagate with arbitrarily large wavevectors within the material volume, thereby enabling optical confinement to exceedingly small dimensions. Indeed, nanometer-scale truncated nanocone hBN cavities, with deeply subwavelength dimensions, have been shown to support three-dimensionally confined optical modes in the mid-infrared. Due to optical selection rules, however, only a few of such modes have been observed experimentally, via far-field reflection and scattering-type scanning near-field optical microscopy. Photothermal induced resonance (PTIR) is an emerging near-field technique that probes optical and vibrational resonances that overcomes the limitations imposed by weak far-field emission by leveraging an AFM probe to transduce local sample expansion induced by light absorption. Here we show that PTIR enables the direct observation of so-far unobserved, dark hyperbolic modes of hBN nanostructures, thus providing unambiguous evidence of their existence. We reason that leveraging such optical modes could yield an unprecedented degree of control over the electromagnetic near-field concentration, polarization and angular momentum, potentially enabling novel nanophotonic applications.
Citation: Nano Letters
Volume: 18
Issue: 3
Pub Type: Journals

Keywords

PTIR, hBN, nanophotonics
Created March 14, 2018, Updated November 10, 2018