Two-dimensional borophene: In-plane hyperbolic polaritons in the visible spectral range

TL;DR

This paper demonstrates the synthesis and characterization of borophene, revealing its unique in-plane hyperbolic polaritonic response in the visible spectrum, which could enable new optoelectronic applications.

Contribution

It introduces a novel synthesis method for borophene with in-plane hyperbolic response in the visible range, supported by experimental and theoretical analysis.

Findings

Borophene exhibits extreme anisotropic optical response in the visible spectrum.

Transition from hyperbolic to elliptic wavefront observed in borophene.

Theoretical calculations confirm experimental observations of borophene's optical properties.

Abstract

Two-dimensional metals, such as graphene, have undergone extensive exploration, with graphene exhibiting a metallic response limited to the infrared spectral range. Overcoming the challenge of extending the electron mobility in two-dimensional metals to achieve plasmonic behaviors in the visible range necessitates innovative synthesis procedures. In this study, we showcase the successful realization of the phase of \c{hi}_3 borophene on diverse substrates using aluminum-based chemical vapor deposition. Leveraging first-principle density-functional theory alongside advanced deep-subwavelength cathodoluminescence spectroscopy, we reveal the extreme anisotropic response of this material in the visible range, transitioning from hyperbolic polaritonic to an elliptic wavefront. Our calculations substantiate the experimental findings, positioning borophene as an unprecedented candidate for the in-plane hyperbolic response in the visible range. These results open avenues for pioneering optoelectronic applications in the visible spectrum, particularly through the incorporation of borophene into hybrid metallic-semiconducting heterostructures.