Ultrafast Nano-Imaging and Optical Control of Hyperbolic Phonon Polaritons at hBN/WS$_2$ Heterojunctions

TL;DR

This paper presents a novel ultrafast nano-imaging technique to observe and control hyperbolic phonon polaritons in heterostructures, enabling femtosecond resolution of light-matter interactions.

Contribution

It introduces a method combining ultrafast infrared near-field microscopy with spectral filtering to achieve nanoscale and femtosecond resolution for polaritonic studies.

Findings

Photocarriers in WS₂ modulate HPhPs in hBN.

Ultrafast imaging reveals dynamic changes in polariton amplitude and wavelength.

Theoretical models confirm dielectric property changes cause observed effects.

Abstract

Manipulating nanoscale light-matter interactions on ultrafast time scales is indispensable for future polaritonic devices. Hyperbolic phonon polaritons (HPhPs) in van der Waals materials enable deep subwavelength confinement of electromagnetic fields in the infrared region and long-distance propagation of polaritonic waves. However, achieving ultrafast imaging and optical control of HPhPs remains a major challenge. Here, we demonstrate the direct observation of transient modulation of HPhPs induced by local photocarrier generation in WS$_2$/hBN heterostructures using ultrafast infrared scanning near-field optical microscopy. We implement grating-based spectral filtering of broadband near-field scattering to simultaneously achieve nanoscale and femtosecond spatiotemporal resolution together with fine spectral selectivity. This ultrafast nano-imaging technique reveals that photocarriers in WS$_2$ modulate the polaritonic field amplitudes and wavelengths of HPhPs in hBN. Theoretical simulations corroborate that these changes arise from photoinduced changes in WS$_2$ dielectric properties. This approach offers a versatile platform for exploring ultrafast polaritonic dynamics at the nanoscale.