Tunable in-plane bi-hyperbolicity in bismuth monolayer

Abstract

The distinctive hyperbolic properties of natural two-dimensional (2D) materials have garnered considerable attention in recent years due to their potential to surpass the limitations of meta-hyperbolic surfaces. It is essential to control hyperbolic regions and the categories of hyperbolicity. In this research, we establish a critical connection between the semiconducting characteristics of 2D materials and their hyperbolic attributes, introducing a concept of “bi-hyperbolicity” using a simple tight-binding model. Based on first-principles calculations, we illustrate how this strategy can be applied to materials like the recently-synthesized bismuth monolayer. Our computations revealed that n-type semiconducting bismuth monolayers exhibit type-I hyperbolicity, whereas p-type semiconducting bismuth monolayers display type-II hyperbolicity. This captivating interplay between hyperbolicity and semiconductivity lays the foundation for crafting in-plane type-I/type-II hyperbolic heterostructures using well-established semiconductor technologies. These heterostructures unlock a plethora of exotic optical phenomena, including negative refraction and negative reflection, which open up new horizons in optical engineering and device design.